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Background: The closure of a pharmacy-led anticoagulation clinic, which provided point-of-care (POC) international normalized ratio (INR) testing and face-to-face visits, coupled with the transition to an academic physician-led clinic without POC INR testing and reliance on telephone communication, created significant challenges for warfarin management during the Coronavirus disease 2019 pandemic. The aim of this quality control project was to increase the percentage of patients on warfarin within the optimal time in therapeutic range (TTR) from 52.30% to 65.00%, sustain baseline quarterly cumulative percentage TTR to 59.00%, and transition 20% of eligible patients from warfarin to dual oral anticoagulation (DOAC) within 12 months., Methods: A multidisciplinary team employed a Fishbone diagram, stakeholder analysis, process flow map, and a driver diagram. Significant barriers included knowledge gaps, fear of blood draws, lack of POC INR testing, and noninteroperable electronic health records (EHRs). Primary outcome measures included quarterly cumulative percentage TTR, 2-monthly percentage TTR, and the percentage of eligible patients switched to DOAC. Process measures included INR completion rates. Key interventions involved educating patients and the care team, transitioning patients to DOAC, improving EHRs, and optimizing processes. Data analysis utilized run charts., Results: Monthly INR completion rates rose from 63% to 87% within 12 months and reached 92% during the 6 months post-project period. Among 143 patients, 40.55% (58) were eligible for a DOAC switch, with 51.72% (30/58) successfully transitioning during the project and the 6-month post-project period. Two-monthly TTR rates improved from the baseline of 52.30% to 62.00% during the study period and remained sustainable at 62.80% in the post-project phase. Quarterly cumulative TTR rates remained stable at 59.20% during the study period in 2021. The quarterly cumulative TTR rates continued to increase at 60.50% and 64.40% in 2022 and 2023, respectively, during the post-project period. No bleeding episodes occurred during the 15-month post-project period., Conclusion: Multi-faceted strategies significantly improved warfarin safety during the project and maintained these improvements for 24 months. Transitioning from warfarin to DOACs was crucial for optimizing anticoagulation management with limited resources. The lead physician and team used various tools to address barriers to effective warfarin management, ensure appropriate DOAC prescribing, and enhance practices for DOAC prescriptions. This project effectively addressed barriers, improved population health, and provided a model for anticoagulation management in primary care settings., (© The Author(s) 2024. Published by Oxford University Press on behalf of International Society for Quality in Health Care. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site–for further information please contact journals.permissions@oup.com.)

Abstract: Anticoagulant therapy can significantly reduce the incidence of stroke and peripheral embolism events in patients with atrial fibrillation (AF). Although warfarin is widely used as an anticoagulant drug, a wrong dose can lead to increased risks of bleeding or blood clots. The aim of this study was to assess whether nuclear factor-erythroid-2-related factor 2 (Nrf2) can improve the efficacy of warfarin through the regulation of cytochrome P450 family 2 subfamily C member 9 (CYP2C9) using a rat model of AF. Results showed that AF significantly reduced Nrf2 in myocardial tissue of sham-operated rats. Furthermore, Nrf2 overexpression effectively reduced AF-induced atrial fibrosis by reducing collagen in the left atrium, inhibiting the expression of the fibrosis-related genes collagen I and transforming growth factor-β1 in rats with AF. Nrf2 overexpression can activate CYP2C9, decrease the serum concentration of warfarin, and decrease prothrombin time and international normalized ratio in AF rats. In this article, Nrf2 overexpression protects against fibrosis, increased survival in AF rats, and activated CYP2C9 expression, thus broadening the therapeutic range of warfarin in AF rats., Competing Interests: The authors report no conflicts of interest., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc.)

Warfarin, with its narrow therapeutic range, requires the understanding of various influencing factors for personalized medication. Vascular senescence, marked by vascular stiffening and endothelial dysfunction, has an unclear effect on the efficacy and safety of warfarin. Based on previous studies, we hypothesized that vascular senescence increases the risk of bleeding during warfarin therapy. This study aimed to explore these effects using animal models and clinical cohorts. We established rat models of vascular senescence and calcification using d-galactose, vitamin D, and nicotine. After validating the models, we examined changes in the international normalized ratio (INR) at fixed warfarin doses (0.20 and 0.35 mg/kg). We found that vascular senescence caused significantly elevated INR values and increased bleeding risk. In the prospective clinical cohort study (NCT06428110), hospitalized warfarin patients with standard dose adjustments were divided into vascular senescence and control groups based on ultrasound and computed tomography diagnosis. Using propensity score matching to exclude the influence of confounding factors, we found that the vascular senescence group had lower steady-state warfarin doses and larger dose adjustments, with a higher probability of INR exceeding the therapeutic range. The vascular senescence group tended to experience more bleeding or thromboembolic/ischemic events during 1 year of follow-up, while there was no statistical difference. In conclusion, vascular senescence leads to unstable INR values and increases higher bleeding risk during warfarin therapy, highlighting the importance of considering vascular senescence in future precision warfarin therapies. SIGNIFICANCE STATEMENT: Many factors influence warfarin efficacy; however, the effect of vascular senescence remains unclear. This study aimed to investigate the effects of vascular senescence on the efficacy and safety of warfarin. Through both rat models and clinical cohort studies, our findings indicated that vascular senescence may compromise the stability of warfarin, presenting challenges in maintaining its efficacy and safety., (Copyright © 2024 by The American Society for Pharmacology and Experimental Therapeutics.)

Warfarin dosing remains challenging due to substantial inter-individual variability, which can lead to unsafe or ineffective therapy with standard dosing. Model-informed precision dosing (MIPD) can help individualize warfarin dosing, requiring the selection of a suitable model. For models developed from clinical data, the dependence on the study design and population raises questions about generalizability. Quantitative system pharmacology (QSP) models promise better extrapolation abilities; however, their complexity and lack of validation on clinical data raise questions about applicability in MIPD. We have previously derived a mechanistic warfarin/international normalized ratio (INR) model from a blood coagulation QSP model. In this article, we evaluated the predictive performance of the warfarin/INR model in the context of MIPD using an external dataset with INR data from patients starting warfarin treatment. We assessed the accuracy and precision of model predictions, benchmarked against an empirically based reference model. Additionally, we evaluated covariate contributions and assessed the predictive performance separately in the more challenging outpatient data. The warfarin/INR model performed comparably to the reference model across various measures despite not being calibrated with warfarin initiation data. Including CYP2C9 and/or VKORC1 genotypes as covariates improved the prediction quality of the warfarin/INR model, even after assimilating 4 days of INR data. The outpatient INR exhibited higher unexplained variability, and predictions slightly exceeded observed values, suggesting that model adjustments might be necessary when transitioning from an inpatient to an outpatient setting. Overall, this research underscores the potential of QSP-derived models for MIPD, offering a complementary approach to empirical model development., (© 2024 The Authors. Clinical Pharmacology & Therapeutics published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

Background: Regarding adjustments to warfarin dosage, numerous studies have shown that computerized methods are superior to those based on personal experience., Objectives: To report the efficacy of a computer-based warfarin management system (WMS) in the Iranian population., Methods: By utilizing the existing dosing algorithms and obtaining expert opinions, we developed a computer-based WMS at a large tertiary cardiovascular center. The time in therapeutic range and the number of international normalized ratio (INR) tests of clinic patients were compared before and after the implementation of WMS., Results: Overall, 803 patients with 5407 INR tests were included in the before phase and 679 patients with 4189 INR tests in the after phase. The mean time in therapeutic range was 57.3% before and 59% after WMS implementation [mean difference, 1.64; 95% confidence interval (CI), -1.12-4.40]. In the before phase, the mean number of INR tests was 6.7, which dropped to 6.1 tests in the after phase (mean difference, -0.61; 95% CI, -0.97 to -0.24). Only 54.5% of the warfarin dosing prescriptions were consistent with the dosing recommendations of the WMS, and adherence to the WMS was poorest in the highest INR target range., Conclusions: For the first time in Iran, we demonstrated that a computerized system was as effective as a traditional experience-based method to monitor INR in VKA-anticoagulated patients. Furthermore, it could reduce both the number of INR tests and that of visits., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Patients with left ventricular assist devices (LVADs) require interruption of warfarin for invasive procedures, but parenteral bridging is associated with many complications. Four-factor prothrombin complex concentrate (4F-PCC) can temporarily restore hemostasis in patients undergoing anticoagulation with warfarin., Objectives: This pilot study evaluated the strategy of using variable-dose 4F-PCC to immediately and temporarily reverse warfarin before invasive procedures without holding warfarin in patients with LVADs. The duration of effect of 4F-PCC on factor levels and time to reestablish therapeutic anticoagulation post procedure were assessed., Methods: Adult patients with LVADs and planned invasive procedures were enrolled from a single center. Warfarin was continued uninterrupted. The 4F-PCC dose administered immediately pre-procedure was based on study protocol. International normalized ratio (INR)- and vitamin K-dependent factor levels were collected before and during the 48 hours after 4F-PCC administration. The use of parenteral bridging, International Society for Thrombosis and Haemostasis major and clinically relevant nonmajor bleeding (CRNMB) and thromboembolic events at 7 and 30 days were collected., Results: In 21 episodes of 4F-PCC reversal, median baseline INR was 2.7 (IQR 2.2-3.2). The median dosage of 4F-PCC administered was 1794 units (IQR 1536-2130). At 24 and 48 hours post 4F-PCC administration, median INRs were 1.8 (IQR 1.7-2.0) and 2.0 (IQR 1.9-2.4). Two patients required postoperative bridging. One patient experienced major bleeding within 72 hours, and 2 experienced CRNMB within 30 days. There were no thromboembolic events. Baseline and post 4F-PCC vitamin K-dependent factor levels corresponded with changes in INR values. The median time to achieve therapeutic INR post-procedure was 2.5 days (IQR, 1-4)., Conclusion: Administration of 4F-PCC for temporary reversal of warfarin for invasive procedures in patients with LVADs allowed for continued warfarin dosing with minimal use of post-intervention bridging, limited bleeding and no thromboembolic events., Competing Interests: Disclosures JMC is a consultant for Abbott, Bristol Myers Squibb, and Pfizer and served on a scientific advisory board for Anthos, Bristol Myers Squibb, Roche, Sanofi, Werfen. MM reports payments made to Brigham and Women's Hospital from Abbott for consulting, consulting fees from Broadview Ventures, Natera, Paragonix, Moderna, and Baim Institute for Clinical Research; he is a scientific advisory board member for NuPulseCV, Leviticus, Transmedics, and FineHeart. MMG, ASW, SS, AEJ, KS, LC, BR have no conflicts to disclose., (Copyright © 2024. Published by Elsevier Inc.)

Objective: Warfarin has a narrow therapeutic window and large variability in dosing that are affected by clinical and genetic factors. To help guide the dosing of warfarin, the Clinical Pharmacogenetics Implementation Consortium has recommended the use of pharmacogenetic algorithms, such as the ones developed by the International Warfarin Pharmacogenetics Consortium (IWPC) and by Gage et al. when genotype information is available., Methods: In this study, simulations were performed in Chinese cohorts to explore how dosing differences between Western (by IWPC and Gage et al.) and Chinese algorithms (by Miao et al.) would mean in terms of anticoagulation effect in clinical trials. We first tried to replicate a published clinical trial comparing genotype-guided dosing to routine clinical dosing in Chinese patients. We then made simulations where Chinese cohorts received daily doses recommended by Gage, IWPC, and Miao algorithms., Results: We found that in simulation conditions where dosing specifications were strictly followed, genotype-guided dosing by IWPC and Lenzini formulae was more likely to overshoot the upper limit of the therapeutic window by day 15, and thus may have a lower % time in therapeutic range (%TTR) than that of clinical dosing group. Also, in comparing Gage, IWPC, and Miao algorithms, we found that the Miao dosing cohort has the highest %TTR and the lowest risk of over-anticoagulation by day 28., Conclusion: In summary, our results confirmed that algorithms developed based on data from local patients may be more suitable for achieving therapeutic international normalized ratio window in Chinese population., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc.)

Background: As direct oral anticoagulants (DOACs) have become widely recommended as first-line anticoagulation therapy, patients who remain on warfarin are likely those unable to afford, adhere to, or utilize DOAC therapy due to the presence of a contraindication. It is currently unknown how availability of DOACs have affected populations being managed at warfarin (VKA) anticoagulation clinics. Methods: This was a retrospective chart review assessing warfarin-treated patients at an outpatient anticoagulation clinic. The primary endpoint was the 6-month time in therapeutic range (TTR) before and after DOACs were recommended as first-line therapy by clinical guidelines. Study periods were January to June 2015, before DOACs were recommended over VKA, and January to June 2022, when DOACs were often recommended over VKA. TTR, demographic changes, and the presence of contraindications to DOAC therapy in the clinic population between the two time periods were assessed. Results: No difference in 6-month TTR was observed between study periods (59% in 2015 vs 63% in 2022; P = .45). Patient demographics did not significantly vary, which may be due to the clinic retaining 45% of patients between both time periods. Contraindications to DOAC therapy were identified in 39% of the 2015 group and 49% of the 2022 group ( P = .18). The most common contraindication was indication for anticoagulation. Conclusion: Availability of DOACs did not seem to significantly affect the population or management of warfarin-treated patients at an outpatient anticoagulation clinic, however, contraindications and potential challenges to use of DOAC therapy are present in many patients., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Background: Little is known how individual time-in-therapeutic-range (TTR) impacts the effectiveness and safety of warfarin therapy compared to direct oral anticoagulants (DOACs) in patients with atrial fibrillation (AF)., Objective: To compare the effectiveness and safety of standard dose DOACs to warfarin in patients with AF, while categorizing warfarin treated patients into quartiles based on their individual TTR., Materials and Methods: We conducted a nationwide study including all patients with new-onset AF between 2011 and 2018 in Finland. Hazard ratios (HR) were calculated using Cox regression analysis with the inverse probability of treatment weighted method to assess the risks of ischaemic stroke (IS), intracranial haemorrhage (ICH) and mortality for users of apixaban ( n  = 12,426), dabigatran ( n  = 4545), rivaroxaban ( n  = 12,950) and warfarin ( n  = 43,548)., Results: The median TTR for warfarin users was 72%. Compared to the second best TTR quartile (reference), the risk of IS was higher in the two poorest TTR quartiles, and lower in the best TTR quartile and on rivaroxaban [2.35 (95% confidence interval, 1.85-2.85), 1.44 (1.18-1.75), 0.60 (0.47-0.77) and 0.72 (0.56-0.92)]. These differences were non-significant for apixaban and dabigatran. HR of ICH was 6.38 (4.88-8.35) and 1.87 (1.41-2.49) in the two poorest TTR groups, 1.44 (1.02-1.93) on rivaroxaban, and 0.58 (0.40-0.85) in the best TTR group compared to the reference group. Mortality was higher in the two poorest TTR groups and lowest in the best TTR group., Conclusions: The outcome was unsatisfactory in the two lowest TTR quartiles - in half of the patients treated with warfarin. The differences between the high TTR groups and standard dose DOACs were absent or modest.

Background : Several studies have examined INR fluctuations using pharmacokinetic (PK) models or post-hoc INR values after completing nirmatrelvir/ritonavir, but further study of the effects of the drug interaction with warfarin during treatment is necessary. Case Summary : Nirmatrelvir/ritonavir is largely utilized in the outpatient setting so data regarding INR trends in hospitalized patients on warfarin is limited. However, many who receive nirmatrelvir/ritonavir outpatient experience difficulty with presenting to clinic for INR checks due to feeling acutely ill along with isolation precautions. We present the case of a patient receiving warfarin and utilizing home INR testing for monitoring. After diagnosis of coronavirus disease of 2019 (COVID-19), she was started on nirmatrelvir/ritonavir on day five after testing positive. Most recent INR prior to the start of therapy was 2.7 and had been stable on the same dose for months prior to infection. On day two of nirmatrelvir/ritonavir, her INR rose to 4.0 on home point of care INR testing. Despite reducing her dose of warfarin by 15%, her INR remained supratherapeutic the day after completing nirmatrelvir/ritonavir (4.0) and for several checks after. One month after completion of therapy, her INR returned to therapeutic levels. Practice Implications : While PK models and case series have hypothesized both potential increases or decreases in INR with the nirmatrelvir/ritonavir and warfarin interaction, COVID-19 infection itself can cause several pharmacodynamic changes which can increase INR, including decreased appetite and, in severe cases, organ dysfunction. This case provides real-world insight into the drug interaction between nirmatrelvir/ritonavir and the drug-disease state interaction between warfarin and COVID-19., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Renal function significantly influences the appropriate warfarin dosage. However, studies investigating the impact of genetic factors on warfarin dosage, considering renal function, are limited. This study aimed to assess the role of genetic polymorphisms in VKORC1 , CYP2C9 , CYP2C19 , CYP4F2 , GGCX , and APOE in warfarin dosage adjustment considering renal function. A total of 108 outpatients receiving warfarin treatment with controlled prothrombin time-targeted international normalized ratio (1.5-3.0) were included. Patient data, warfarin dosage, and laboratory results were collected from electronic medical records. Each SNP [ VKORC1 rs9923231, CYP2C9 rs1057910, CYP4F2 rs2108622, CYP2C19 * 2 (rs4244285) and * rs7421] was analyzed. Multiple regression analysis revealed estimated glomerular filtration rate as the most significant factor influencing warfarin dose (p <0.001) ( 3 (rs4986893), GGCX rs699664 and rs12714145, and APOE rs7421] was analyzed. Multiple regression analysis revealed estimated glomerular filtration rate as the most significant factor influencing warfarin dose (p <0.001) ( β = -0.445). VKORC1 rs1057910 AC carriers were associated with warfarin dose (p <0.001, 0.015, 0.020, 0.038 and β = -0.317, 0.191, -0.188, -0.162, respectively); however, other genes showed no significant association. In conclusion, after adjusting for renal function, genetic factors of CYP4F2 rs2108622 CT/TT, GGCX rs12714145 CT/TT, and CYP2C9 rs1057910 AC carriers were associated with warfarin dose (p <0.001, 0.015, 0.020, 0.038 and β = -0.317, 0.191, -0.188, -0.162, respectively); however, other genes showed no significant association. In conclusion, after adjusting for renal function, genetic factors of VKORC1 rs1057910 were found to contribute to warfarin dosage, having impact in that order. In contrast, the contribution of other genes to warfarin dosage was absent or negligible.CYP4F2 rs2108622, GGCX rs12714145, and CYP2C9 rs1057910 were found to contribute to warfarin dosage, having impact in that order. In contrast, the contribution of other genes to warfarin dosage was absent or negligible.

In the era of direct oral anticoagulants, vitamin K antagonists retain a clinically relevant role in thrombotic disorders. In Italy, approximately 20% of the patients on anticoagulant therapies receives a VKA, in most cases warfarin. The optimal management of this drug is challenging and cannot disregard its intricate and unpredictable pharmacokinetic properties and patient's thrombotic and bleeding risk. Several clinical issues encountered during warfarin treatment are still unanswered and are tentatively addressed by physicians. In this regard, the Italian Federation of Centers for the diagnosis of thrombotic disorders and the Surveillance of the Antithrombotic therapies (FCSA) provides some experience-based good clinical practice's suggestions on the following topics: (1) how to start the anticoagulant treatment with warfarin and warfarin induction regimen; (2) how to manage a subtherapeutic INR value; (3) how to manage a supratherapeutic INR value in asymptomatic patients; and (4) how to manage the association of warfarin with interfering drugs., Competing Interests: S.G. received honoraria for speaking at symposia from Pfizer and Daiichi-Sankyo and supports for attending meetings from Bayer, Daiichi-Sankyo, and Pfizer. P. B. received honoraria for lectures and/or participation on advisory board from Daiichi Sankyo, Pfizer, Bristol-Myers Squibb, Astra-Zeneca, Exeltis. D.B. received honoraria for lectures from Aspen and Werfen. C.A. received honoraria for lectures from Bayer. E.G. received honoraria for lectures from Sanofi and Italfarmaco, and for participation on advisory board from Roche, Sanofi Genzyme, and Novo Nordisk. G.M. received honoraria for lectures and for participation on advisory board: Bayer, Roche, Exeltis. G.R. declares no conflict of interest; A.S. received honoraria for lectures, manuscript writing, and/or participation on advisory board from Daiichi Sankyo, Bayer, Pfizer, Bristol-Myers Squibb, Boehringer Ingelheim, Sanofi, Werfen, Viatris, Alexion, and Roche. V.T. declared no conflict of interest. S.T. received honoraria for lectures and for participation on advisory board from Werfen, Stago, Italfarmaco, Pfizer, Bristol-Myers Squibb, and Sanofi. D.P. received honoraria for educational events from Pfizer, Daiichi-Sankyo, and Boehringer., (The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/).)

Background: Poor anticoagulation management of warfarin may lead to patient admission, prolonged hospital stays, and even death due to anticoagulation-related adverse events. Traditional non-web-based outpatient clinics struggle to provide ideal anticoagulation management services for patients, and there is a need to explore a safer, more effective, and more convenient mode of warfarin management., Objective: This study aimed to compare differences in the quality of anticoagulation management and clinical adverse events between a web-based management model (via a smartphone app) and the conventional non-web-based outpatient management model., Methods: This study is a prospective cohort research that includes multiple national centers. Patients meeting the nadir criteria were split into a web-based management group using the Alfalfa app or a non-web-based management group with traditional outpatient management, and they were then monitored for a 6-month follow-up period to collect coagulation test results and clinical events. The effectiveness and safety of the 2 management models were assessed by the following indicators: time in therapeutic range (TTR), bleeding events, thromboembolic events, all-cause mortality events, cumulative event rates, and the distribution of the international normalized ratio (INR)., Results: This national multicenter cohort study enrolled 522 patients between June 2019 and May 2021, with 519 (99%) patients reaching the follow-up end point, including 260 (50%) in the non-web-based management group and 259 (50%) in the web-based management group. There were no observable differences in baseline characteristics between the 2 patient groups. The web-based management group had a significantly higher TTR than the non-web-based management group (82.4% vs 71.6%, P<.001), and a higher proportion of patients received effective anticoagulation management (81.2% vs 63.5%, P<.001). The incidence of minor bleeding events in the non-web-based management group was significantly higher than that in the web-based management group (12.1% vs 6.6%, P=.048). Between the 2 groups, there was no statistically significant difference in the incidence of severe bleeding and thromboembolic and all-cause death events. In addition, compared with the non-web-based management group, the web-based management group had a lower proportion of INR in the extreme subtreatment range (17.6% vs 21.3%) and severe supertreatment range (0% vs 0.8%) and a higher proportion in the treatment range (50.4% vs 43.1%), with statistical significance., Conclusions: Compared with traditional non-web-based outpatient management, web-based management via the Alfalfa app may be more beneficial because it can enhance patient anticoagulation management quality, lower the frequency of small bleeding events, and improve INR distribution., (©Wenfei Chen, Jiana Chen, Shaojun Jiang, Chunhua Wang, Jinhua Zhang. Originally published in the Journal of Medical Internet Research (https://www.jmir.org), 29.07.2024.)

Warfarin-related nephropathy (WRN) is defined as acute kidney injury subsequent to excessive anticoagulation with warfarin. Patients with mechanical prosthetic valves require long-term anticoagulant therapy. Nonetheless, warfarin remains the sole available option for anticoagulant therapy. Consequently, patients with mechanical prosthetic valves constitute a special group among the entire anticoagulant population. The present study recorded two cases of patients who had undergone mechanical prosthetic valve surgery and were receiving warfarin therapy. They presented to the hospital with gross hematuria and progressive creatinine levels. Notably, their international normalized ratio (INR) did not exceed three. Subsequent renal biopsies confirmed WRN with IgA nephropathy. The two patients continued to receive warfarin as anticoagulation therapy and were prescribed oral corticosteroids and cyclophosphamide, which resulted in improved renal function during the follow-up. Based on a review of all relevant literature and the present study, we proposed a new challenge: must elevated INR levels be one of the criteria for clinical diagnosis of WRN? Perhaps some inspiration can be drawn from the present article., (© 2024. The Author(s).)

Background: The continuation of long-term warfarin therapy is gaining acceptance in minor surgeries but maintaining therapeutic international normalized ratio (INR) values among patients during major orthopedic procedures raises concern. While bridging therapy with low-molecular-weight heparin is currently recommended for patients receiving anticoagulation, few studies have evaluated the safety of continuing warfarin during total joint arthroplasty. This study evaluated the safety and efficacy of continuous warfarin anticoagulation through total joint arthroplasty with and without prophylactic tranexamic acid (TXA)., Materials and Methods: We conducted a retrospective, matched-pair analysis of two experimental groups of patients who underwent primary total hip arthroplasty or total knee arthroplasty performed by a single surgeon. Our first experimental group, warfarin plus TXA (warfarin+TXA), consisted of 21 patients who underwent arthroplasty while receiving therapeutic anticoagulation with warfarin (INR, 2.0-3.0) and who received prophylactic TXA. Our second experimental group, warfarin without TXA (warfarin-TXA), consisted of 40 patients who underwent arthroplasty while receiving therapeutic anticoagulation with warfarin (INR, 2.0-3.0) without prophylactic TXA., Results: The percent change in hemoglobin value after surgery, red blood cells transfused, surgical site infections, bleeding complications, and thrombotic complications were similar between both experimental and control groups. When comparing the historical group with the warfarin+TXA group, the addition of TXA resulted in a statistical decrease in mean red blood cells transfused and estimated blood loss, with no statistically significant increase in complications., Conclusion: Many factors must be considered when choosing perioperative thromboembolic prophylaxis for arthroplasty candidates with medical comorbidities requiring long-term anticoagulation. This study presents data indicating that it could be safe and effective to continue therapeutic warfarin while using prophylactic TXA. [ Orthopedics . 2024;47(4):211-216.].

Background: Thrombolytic therapy is effective method in the high-risk acute pulmonary embolism (PE) treatment. Reduced-dose thrombolysis (RDT) plus oral anticoagulation therapy is effective and safe method in the moderate and severe PE treatment. It is leading to good early and intermediate-term outcomes. In the RE-COVER and RE-COVER II studies, dabigatran showed similar effectiveness as warfarin in the treatment of acute PE. Dabigatran leads to fewer hemorrhagic complications and is not inferior in efficacy to warfarin in the prevention of PE after mechanical fragmentation and RDT (catheter-directed treatment [CDT]+RDT) in patients with high and intermediate to high PE risk. We sought to evaluate the efficacy and safety (incidence of clinically significant recurrence of venous thromboembolic complications and deaths) during a 6-month course of treatment with dabigatran or warfarin in patients with high and intermediate to high acute PE risk after endovascular mechanical thrombus fragmentation procedure with RDT (CDT+RDT)., Methods: The RE-SPIRE is a prospective, multicenter randomized double-arm study. Over a 5-year period, 66 consecutive patients with symptomatic high and intermediate to high PE risk after endovascular mechanical thrombus fragmentation procedure with RDT (CDT+RDT) were randomized into two groups within the next 48 hours. The first group continued treatment with dabigatran 150 mg twice a day for 6 months; the second group continued treatment with warfarin under the control of international normalized ratio (2.0-3.0) for 6 months. Both groups received low molecular weight heparins for 2 days after surgery. Then, group 1 continued to receive low molecular-weight-heparin for 5 to 7 days, followed by a switch to dabigatran at a dosage of 150 mg two times a day. Group 2 received both low-molecular-weight heparin and warfarin up to an international normalized ratio of >2.0, followed by heparin withdrawal. The follow-up period was 6 months., Results: There were 63 patients who completed the study (32 in the dabigatran group and 31 in the warfarin group). In both groups, there was a statistically significant decrease in the mean pulmonary artery pressure. The mean pulmonary artery pressure at the 6-month follow-up after surgery was 24 mm Hg (interquartile range, 20.3-29.25 mm Hg) in the dabigatran group and 23 mm Hg (interquartile range, 20.0-26.3 mm Hg) in the warfarin group. The groups did not differ statistically in the deep vein thrombosis dynamics. Partial recanalization occurred in 52.0% vs 73.1% in the dabigatran and warfarin groups, respectively (P = .15). Complete recanalization occurred in 28.0% vs 19.2% in the dabigatran and warfarin groups, respectively (P = .56). The groups did not differ in the frequency of major bleeding events according to the International Society for Thrombosis and Hemostasis (0% vs 3.2% in the dabigatran and warfarin groups, respectively; P = 1.00). However, there were more nonmajor bleeding events in the warfarin group than in the dabigatran group (16.1% vs 0%, respectively; P = .02)., Conclusions: The results of the study show that dabigatran is comparable in effectiveness to warfarin. Dabigatran has greater safety in comparison with warfarin in the occurrence of all cases of bleeding in the postoperative and long-term periods. Thus, dabigatran may be recommended for the treatment and prevention of PE after CDT with RDT in patients with high and intermediate to high PE risk., Competing Interests: Disclosures None., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

The purpose of this paper is to study the genetic polymorphisms of related gene loci (CYP2C9*3, VKORC1-1639G > A) based on demographic and clinical factors, and use the maximum a posterior Bayesian method to construct a warfarin individualized dose prediction model in line with the Chinese Han population. Finally, the built model is compared and analyzed with the widely used models at home and abroad. In this study, a total of 5467 INR measurements are collected from 646 eligible subjects in our hospital, and the maximum a posterior Bayesian method is used to construct a warfarin dose prediction that conforms to the Chinese Han population on the basis of the Hamberg model. The model is verified and compared with foreign models. This study finds that body weight and concomitant use of amiodarone have a significant effect on the anticoagulant effect of warfarin. The model can provide an effective basis for individualized and rational dosing of warfarin in Han population more accurately. In the performance of comparison with different warfarin dose prediction models, the new model has the highest prediction accuracy, and the prediction percentage is as high as 72.56%. The dose predicted by the Huang model is the closest to the actual dose of warfarin. The population pharmacokinetics and pharmacodynamics model established in this study can better reflect the distribution characteristics of INR values after warfarin administration in the Han population, and performs better than the models reported in the literature., (© 2024. The Author(s).)

The quality of warfarin treatment may be improved if management is guided by the use of models based upon pharmacokinetic-pharmacodynamic theory. A prospective, two-armed, single-blind, randomized controlled trial compared management aided by a web-based dose calculator (NextDose) with standard clinical care. Participants were 240 adults receiving warfarin therapy following cardiac surgery, followed up until the first outpatient appointment at least 3 months after warfarin initiation. We compared the percentage of time spent in the international normalized ratio acceptable range (%TIR) during the first 28 days following warfarin initiation, and %TIR and count of bleeding events over the entire follow-up period. Two hundred thirty-four participants were followed up to day 28 (NextDose: 116 and standard of care: 118), and 228 participants (114 per arm) were followed up to the final study visit. Median %TIR tended to be higher for participants receiving NextDose guided warfarin management during the first 28 days (63 vs. 56%, P = 0.13) and over the entire follow-up period (74 vs. 71%, P = 0.04). The hazard of clinically relevant minor bleeding events was lower for participants in the NextDose arm (hazard ratio: 0.21, P = 0.041). In NextDose, there were 89.3% of proposed doses accepted by prescribers. NextDose guided dose management in cardiac surgery patients requiring warfarin was associated with an increase in %TIR across the full follow-up period and fewer hemorrhagic events. A theory-based, pharmacologically guided approach facilitates higher quality warfarin anticoagulation. An important practical benefit is a reduced requirement for clinical experience of warfarin management., (© 2024 The Authors. Clinical Pharmacology & Therapeutics published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

Different dosing strategies exist to initiate warfarin, most commonly fixed warfarin dosing (FWD), clinical warfarin dosing (CWD), and genetic-guided warfarin dosing (GWD). Landmark trials have shown GWD to be superior when compared to FWD in the EU-PACT trial or CWD in the GIFT trial. COAG trial did not show differences between GWD and CWD. We aim to compare the anticoagulation quality outcomes of CWD and FWD. This is a prospective cohort study with a retrospective comparator. Recruited subjects in the CWD (prospective) arm were initiated on warfarin according to the clinical dosing component of the algorithm published in www.warfarindosing.org. The primary efficacy outcome was the percentage time in the therapeutic range (PTTR) from day 3 to 6 till day 28 to 35. The study enrolled 122 and 123 patients in the CWD and FWD, respectively. The PTTR did not differ statistically between CWD and FWD (62.2 ± 26.2% vs. 58 ± 25.4%, p = 0.2). There was also no difference between both arms in the percentage of visits with extreme subtherapeutic international normalized ratio (INR) (<1.5; 15 ± 18.3% vs. 16.8 ± 19.1%, p = 0.44) or extreme supratherapeutic INR (>4; 7.7 ± 14.7% vs. 7.5 ± 12.4%, p = 0.92). We conclude that CWD did not improve the anticoagulation quality parameters compared to the FWD method., (© 2024 Qatar University. Clinical and Translational Science published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

Non-activated four-factor prothrombin complex concentrate (4 F-PCC) has emerged as the preferred reversal strategy for patients on warfarin with life-threatening bleeding. Current dosing recommendations for 4 F-PCC require pre-treatment international normalized ratio (INR) and bodyweight values, resulting in ordering and administration delays. Studies have shown that alternative dosing regimens are safe and efficacious. This retrospective, single-center, pre- and post-protocol analysis was conducted to assess the efficacy of a pharmacist driven modified fixed-dose 4 F-PCC regimen versus package insert weight- and INR-based dosing regimen for warfarin reversal. The primary outcome was achievement of INR less than two. Secondary outcomes included dose and cost of 4 F-PCC, a time analysis, incidence of concomitant vitamin K administration, and incidence of thrombosis within seven days of 4 F-PCC. There were 195 patients included in the analysis, with 74 in the pre-cohort and 121 in the post-cohort. Baseline characteristics were similar between cohorts with the most common indication for warfarin use being atrial fibrillation (48.6% versus 47.1%) and reversal being intracerebral hemorrhage (68.9% versus 43.0%). Achievement of the primary endpoint occurred in 92% versus 95% (p = 0.097) of patients. A statistically significant difference was seen between cohorts regarding median dose and cost of 4 F-PCC administered (p < 0.001). Eleven thromboembolic events occurred with three events in the pre-cohort and eight events in the post-cohort (p = 0.453). A fixed-dose of 1500IU of 4 F-PCC was effective in reversing INR to less than two in most patients regardless of reversal indication with minimal thrombotic risks., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Objectives: To evaluate if there is a difference in International Normalized Ratio (INR) readings taken within the 15 second time frame after lancing the finger vs 30-60 seconds of obtaining a blood drop utilizing a CoaguChek ® XS Plus point-of-care (POC) INR machine in patients on warfarin therapy. Methods: All adult patients on anticoagulation therapy with warfarin who were managed in a pharmacist-run anticoagulation clinic were considered for inclusion in the study. The mean difference of INR readings taken less than 15 seconds vs between 30-60 seconds after the blood drop was obtained from the finger was assessed. Results: A total of 62 pairs of INR results were included in the study. There was a mean difference in INR of .076 (95% CI 0.011-.140; P = .0217) when comparing INR readings taken less than 15 seconds and between 30-60 seconds after the blood drop was obtained from the finger. Conclusions: There was a significant difference in INR readings taken less than 15 seconds vs 30-60 seconds after obtaining the blood drop when utilizing a POC INR machine. INR readings taken 30-60 seconds after obtaining a blood drop with the CoaguChek ® XS Plus POC INR machine is not acceptable for use to monitor patients on warfarin., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Background: Empirical use of pharmacogenetic test(PGT) is advocated for many drugs, and resource-rich setting hospitals are using the same commonly. The clinical translation of pharmacogenetic tests in terms of cost and clinical utility is yet to be examined in hospitals of low middle income countries (LMICs)., Aim: The present study assessed the clinical utility of PGT by comparing the pharmacogenetically(PGT) guided- versus standard of care(SOC)- warfarin therapy, including the health economics of the two warfarin therapies., Methods: An open-label, randomized, controlled clinical trial recruited warfarin-receiving patients in pharmacogenetically(PGT) guided- versus standard of care(SOC)- study arms. Pharmacogenetic analysis of CYP2C9*2(rs1799853), CYP2C9*3(rs1057910) and VKORC1(rs9923231) was performed for patients recruited to the PGT-guided arm. PT(Prothrombin Time)-INR(international normalized ratio) testing and dose titrations were allowed as per routine clinical practice. The primary endpoint was the percent time spent in the therapeutic INR range(TTR) during the 90-day observation period. Secondary endpoints were time to reach therapeutic INR(TRT), the proportion of adverse events, and economic comparison between two modes of therapy in a Markov model built for the commonest warfarin indication- atrial fibrillation., Results: The study enrolled 168 patients, 84 in each arm. Per-protocol analysis showed a significantly high median time spent in therapeutic INR in the genotype-guided arm(42.85%; CI 21.4-66.75) as compared to the SOC arm(8.8%; CI 0-27.2)(p < 0.00001). The TRT was less in the PG-guided warfarin dosing group than the standard-of-care dosing warfarin group (17.85 vs. 33.92 days) (p = 0.002). Bleeding and thromboembolic events were similar in the two study groups. Lifetime expenditure was ₹1,26,830 in the PGT arm compared to ₹1,17,907 in the SOC arm. The QALY gain did not differ in the two groups(3.9 vs. 3.65). Compared to SOC, the incremental cost-utility ratio was ₹35,962 per QALY gain with PGT test opting. In deterministic and probabilistic sensitivity analysis, the base case results were found to be insensitive to the variation in model parameters. In the cost-effectiveness-acceptability curve analysis, a 90% probability of cost-effectiveness was reached at a willingness-to-pay(WTP) of ₹ 71,630 well below one time GDP threshold of WTP used., Conclusion: Clinical efficacy and the cost-effectiveness of the warfarin pharmacogenetic test suggest its routine use as a point of care investigation for patient care in LMICs., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Warfarin remains the most prescribed oral anticoagulant of choice in atrial fibrillation (AF) patient in resource-limited settings. Despite evidence linking Time in Therapeutic Range (TTR) to patient outcomes, its use in clinical practice is not widespread. This prospective study explores the impact of a TTR-INR guided Warfarin adjustment protocol on TTR in AF patients. Conducted at the Warfarin clinic of King Chulalongkorn Memorial Hospital. TTR was calculated using the Rosendaal linear interpolation method at baseline, and then at 6 and 12 months post-protocol implementation. The primary outcome was the improvement in TTR following the protocol's implementation. The study analyzed 57 patients, with a mean age of 72 years and an even gender distribution. At baseline, 53% of patients had a TTR of less than 65%. However, TTR significantly improved from 65% at baseline to 80% after 12 months of protocol implementation (p < 0.001). Furthermore, there was a significant increase in the proportion of patients with a TTR of 65% or more, from 47 to 88% (p < 0.001). During the follow-up period in the first 12 months, three patients died, but no ischemic or major bleeding events occurred. The significant improvement in TTR after 12 months of protocol implementation suggests that this strategy could provide additional value in improving TTR and outcomes in AF patients receiving Warfarin., (© 2024. The Author(s).)

Warfarin, a widely utilized anticoagulant, is paramount for preventing thromboembolic events in patients with mechanical heart valve replacements. However, its narrow therapeutic index can lead to over-anticoagulation and overdose, resulting in serious health risks. This study examines the efficacy of human prothrombin complex concentrate (PCC) in managing warfarin overdose, in comparison with traditional treatments. A retrospective analysis was conducted on 162 adults who presented with warfarin overdose (INR > 5.0) at a tertiary care hospital between 2016 and 2020. Participants were divided into 2 groups-those treated with PCC (n = 57) and those treated with conventional methods (n = 105), including vitamin K and fresh frozen plasma. The primary outcome was the rate of reaching the target (International Normalized Ratio) INR within 24 hours. Secondary outcomes included transfusion requirements, thromboembolic events, adverse reactions, 30-day mortality, and length of hospital stay. PCC demonstrated significant efficacy, with 89.5% of patients achieving the target INR within 24 hours, compared to 64.8% in the control group (P < .05). The PCC group also had reduced transfusion requirements and a shorter average hospital stay. There was no significant difference in thromboembolic events or adverse reactions between the 2 groups, and the reduced 30-day mortality in the PCC group was not statistically significant. Human prothrombin complex concentrate is associated with rapid reaching the target INR, decreased transfusion needs, and shortened hospitalization, making it a promising option for warfarin overdose management. While the results are encouraging, larger, multicenter, randomized controlled trials are necessary to further validate these findings and optimize PCC administration protocols., Competing Interests: The authors have no funding and conflicts of interest to disclose., (Copyright © 2024 the Author(s). Published by Wolters Kluwer Health, Inc.)

Objectives: To assess if warfarin targeted to international normalized ratio (INR) 1.8 (range 1.5-2.0) is safe for all patients with an On-X aortic mechanical valve., Methods: This prospective, observational registry follows patients receiving warfarin targeted at an INR of 1.8 (range 1.5-2.0) plus daily aspirin (75-100 mg) after On-X aortic valve replacement. The primary end point is a composite of thromboembolism, valve thrombosis and major bleeding. Secondary end points include the individual rates of thromboembolism, valve thrombosis and major bleeding, as well as the composite in subgroups of home or clinic-monitored INR and risk categorization for thromboembolism. The control was the patient group randomized to standard-dose warfarin (INR 2.0-3.0) plus daily aspirin 81 mg from the PROACT trial., Results: A total of 510 patients were enroled at 23 centres in the UK, USA and Canada. Currently, the median follow-up duration is 3.4 years, and median achieved INR is 1.9. The primary composite end point rate in the low INR patients is 2.31% vs 5.39% (95% confidence interval 4.12-6.93%) per patient-year in the PROACT control group, constituting a 57% reduction. Results are consistent in subgroups of home or clinic-monitored, and high-risk patients, with reductions of 56%, 57% and 57%, respectively. Major and total bleeding are decreased by 85% and 73%, respectively, with similar rates of thromboembolic events. No valve thrombosis occurred., Conclusions: Interim results suggest that warfarin targeted at an INR of 1.8 (range 1.5-2.0) plus aspirin is safe and effective in patients with an On-X aortic mechanical valve with or without home INR monitoring., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery.)

Warfarin is a widely used anticoagulant, and its S-enantiomer has higher potency compared to the R-enantiomer. S-warfarin is mainly metabolized by cytochrome P450 (CYP) 2C9, and its pharmacological target is vitamin K epoxide reductase complex subunit 1 (VKORC1). Both CYP2C9 and VKORC1 have genetic polymorphisms, leading to large variations in the pharmacokinetics (PKs) and pharmacodynamics (PDs) of warfarin in the population. This makes dosage management of warfarin difficult, especially in the case of drug-drug interactions (DDIs). This study provides a whole-body physiologically-based pharmacokinetic/PD (PBPK/PD) model of S-warfarin for predicting the effects of drug-drug-gene interactions on S-warfarin PKs and PDs. The PBPK/PD model of S-warfarin was developed in PK-Sim and MoBi. Drug-dependent parameters were obtained from the literature or optimized. Of the 34 S-warfarin plasma concentration-time profiles used, 96% predicted plasma concentrations within twofold range compared to observed data. For S-warfarin plasma concentration-time profiles with CYP2C9 genotype, 364 of 386 predicted plasma concentration values (~94%) fell within the twofold of the observed values. This model was tested in DDI predictions with fluconazole as CYP2C9 perpetrators, with all predicted DDI area under the plasma concentration-time curve to the last measurable timepoint (AUC last ) ratio within twofold of the observed values. The anticoagulant effect of S-warfarin was described using an indirect response model, with all predicted international normalized ratio (INR) within twofold of the observed values. This model also incorporates a dose-adjustment method that can be used for dose adjustment and predict INR when warfarin is used in combination with CYP2C9 perpetrators., (© 2024 The Authors. CPT: Pharmacometrics & Systems Pharmacology published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

Background/aims: The SAMe-TT2R2 score is used for assessing anticoagulation control (AC) quality with warfarin. However, it is hard to apply SAMe-TT2R2 score in Asian patients with atrial fibrillation (AF), because it has not been proven in those populations. This study aimed to validate the SAMe-TT2R2 score in Asian patients with AF and suggest a modified SAMe- TT2R2 score for this population., Methods: We analyzed 710 Korean patients with AF who were using warfarin. The AC quality was assessed as the mean time in therapeutic range (TTR). Each component of SAMe-TT2R2 score was evaluated for the relationship with AC. Further clinical factors that predict AC were analyzed. Identified factors were re-assorted and constructed as SA2Me-TTR scoring system., Results: Of the components of the SAMe-TT2R2 score, female, age, and rhythm control were associated with AC. Heart failure and renal insufficiency were newly identified factors associated with AC. The modified SA2Me-TTR score was reconstructed with the relevant risk factors (S, female gender, 1 point; A, age < 60 yr, 2 points; Me, medical history of heart failure, 1 point; T, treatment for rhythm control, 1 point; T, history of stroke or transient ischemic attack, 1 point; R, renal insufficiency, 1 point). The modified SA2Me-TTR score demonstrated an excellent relationship with the grading of AC. The modified SA2Me-TTR score ≤ 1 identified patients with good AC (hazard ratio 2.46, 95% CI 1.75-3.47)., Conclusion: The modified SA2Me-TTR score was useful for guiding oral anticoagulants selection in Asian patients with AF.

Background: Warfarin is widely used for the prevention and treatment of thrombotic events. This study aimed to examine the influence of gene polymorphisms on the early stage of warfarin therapy in patients following heart valve surgery., Methods: Nine single nucleotide polymorphisms were genotyped using microarray chips, categorizing patients into three groups: normal responders (Group I), sensitive responders (Group II), and highly sensitive responders (Group III). The primary clinical outcomes examined were time in therapeutic range (TTR) and international normalized ratio (INR) variability. To investigate potential influencing factors, a generalized linear regression model was employed., Results: Among 734 patients, the prevalence of CYP2C9*3-1075A > C, CYP2C19*3-636G > A, and CYP2C19*17-806C > T variants were 11.2%, 9.9%, and 1.9% of patients, respectively. VKORC1-1639G > A or the linked -1173C > T variant was observed in 99.0% of the patients. Generalized linear model analysis revealed an impact of sensitivity grouping on INR variability. Compared to Group I, Group II showed higher TTR values (p = 0.023), while INR variability was poorer in Group II (p < 0.001) and Group III (p < 0.001). Individual gene analysis identified significant associations between CYP2C9*3-1075A > C (p < 0.001), VKORC1-1639G > A or the linked -1173 C > T (p = 0.009) and GGCX-3261G > A (p = 0.019) with INR variability., Conclusion: The genotypes of CYP2C9, VKORC1, and GGCX were found to have a significant impact on INR variability during the initial phase of warfarin therapy. However, no significant association was observed between TTR and gene polymorphisms. These findings suggest that focusing on INR variability is crucial in clinical practice, and preoperative detection of gene polymorphisms should be considered to assist in the initiation of warfarin therapy., (© 2024. The Author(s) under exclusive licence to Maj Institute of Pharmacology Polish Academy of Sciences.)

Warfarin is the only oral anticoagulant recommended in women who are breastfeeding. Although warfarin is a compatible and recommended agent in the postpartum period and during lactation, little is known regarding changes to warfarin dose requirements in this patient population. Here, we report the case of a 40-year-old woman who transitioned from enoxaparin monotherapy back to warfarin at 2 months postpartum, while she was breastfeeding. Despite resuming warfarin at her previously therapeutic dose, her international normalized ratio (INR) remained subtherapeutic and required multiple dose increases. She ultimately required a 100% increase in her warfarin dose postpartum, compared to pre-pregnancy, to achieve a therapeutic INR. This case suggests patients may require higher warfarin doses postpartum, compared to pre-pregnancy, especially if breastfeeding. Clinicians should closely monitor these patients and adjust warfarin doses as necessary., (© 2024 The Authors. Pharmacotherapy: The Journal of Human Pharmacology and Drug Therapy published by Wiley Periodicals LLC on behalf of Pharmacotherapy Publications, Inc.)

Vaccines against SARS-CoV-2 have been recommended across the world, yet no study has investigated whether COVID-19 vaccination influences short-term warfarin anti-coagulation levels. Patients on stable warfarin treatment who received anti-SARS-CoV-2 vaccination were prospectively enrolled and followed up for three months. INR values less than 10 days before vaccination (baseline), 3-5 days (short-term) and 6-14 days (medium-term) after vaccination were recorded as INR0, INR1, and INR2, respectively. The variations of INR values within individuals were compared, and the linear mixed effect model was used to evaluate the variations of INR values at different time points. Logistic regression analysis was performed to determine covariates related to INR variations after COVID-19 vaccination. Vaccination safety was also monitored. There was a significant difference in INR values between INR0 and INR1 (2.15 vs. 2.26, p = 0.003), yet no marked difference was found between INR0 and INR2. The linear mixed effect model also demonstrated that INR variation was significant in short-term but not in medium-term or long-term period after vaccination. Logistic regression analysis showed that no investigated covariates, including age, vaccine dose, genetic polymorphisms of VKORC1 and CYP2C9 etc., were associated with short-term INR variations. Two patients (2.11%) reported gingival hemorrhage in the short-term due to increased INR values. The overall safety of COVID-19 vaccines for patients on warfarin was satisfying. COVID-19 vaccines may significantly influence warfarin anticoagulation levels 3-5 days after vaccination. We recommend patients on warfarin to perform at least one INR monitoring within the first week after COVID-19 vaccination., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Purpose: Warfarin is effective therapy to prevent thromboembolic complications of venous thromboembolism, atrial fibrillation, and cardiac thrombus, among valvular heart diseases, including in patients treated with prostheses and/or repair. Its optimum effect is achieved when the international normalized ratio (INR) is in the target therapeutic range, but a subtherapeutic level increases risk of thromboembolism and complications. This study aimed to assess the attainment of target therapeutic range, proportion, and factors associated with subtherapeutic level of warfarin., Methods: A hospital-based cross-sectional study was conducted at Jimma Medical Center in Jimma, Ethiopia, from October 1, 2020 through December 30, 2021. All patients on warfarin and attending Medical Follow-Up Clinics of Jimma Medical Center during the study period were included. Data were collected using structured questionnaires and then analyzed using EpiData Manager software, version 3.1 (EpiData Association). χ 2 Tests and logistic regression models were used to assess relationships among variables., Findings: Of 196 patients on warfarin, ∼60% were taking it for atrial fibrillation, followed by deep venous thrombosis, women accounted for 61.7% of patients, and mean (SD) age was 43 (7) years. Most patients (61.7%) lived in rural areas and 44.9% farmed to earn a living. Most of the study participants (51.5%) had a very low monthly income of less than USD50. Most of the patients (n = 107 [54.6%]) were advised on dietary selections while on warfarin and approximately two-thirds (n = 70 [65.4%]) were adherent to the advice. Most participants (n = 118 [60.2%]) were poorly adherent to warfarin therapy and more than two-thirds of them discontinued warfarin for financial reasons. Mean (SD) duration of warfarin therapy was 15.53 (18.92) months (range 1-90 months). Most of the respondents (n = 109 [55.6%]) had subtherapeutic INR and 21 (10.7%) were in the supratherapeutic range. Although the mean (SD) time in therapeutic range was 25.03% (24.17% [range 0-80%]), in most patients (n = 166 [84.7%]), it was <60%. Poor adherence (adjusted odds ratio = 6.13; 95% CI, 3.31-28.10), shorter duration of warfarin (<12 months; adjusted odds ratio = 0.104; 95% CI, 0.012-0.875), and presence of comorbidity (adjusted odds ratio = 0.035; 95% CI, 0.004-0.323) were significantly associated with subtherapeutic INR., Implications: Attainment of therapeutic INR among patients on warfarin therapy is suboptimal. This was evidenced by a significant number of patients with low time in therapeutic range, as well as INR. Poor adherence to warfarin therapy, shorter duration since initiation of warfarin, and presence of comorbid illnesses were significantly associated with subtherapeutic INR. This can lead to complications of atrial fibrillation, including thrombus formation and subsequent cardioembolic stroke, venous thromboembolism, and others, leading to morbidity, increased mortality, and poor quality of life. Therefore, providing health education and treatment for comorbidities may improve adherence, which may also improve attainment of therapeutic INR and reduce complications and improve quality of life., Competing Interests: Declaration of competing interest None declared., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Aims: Genotype-guided dosing algorithms can explain about half of the interindividual variability in prothrombin time-international normalized ratio (PT-INR) under warfarin treatment. This study aimed to refine a published kinetic-pharmacodynamic model and guide warfarin dosage for an optimal PT-INR based on renal function., Methods: Using a retrospective cohort of adult patients (>20 years) who were administered warfarin and underwent PT-INR measurements, we refined the kinetic-pharmacodynamic model with age and the genotypes of cytochrome P450 2C9 and vitamin K epoxide reductase complex subunit 1 using the PRIOR subroutine in the nonlinear-mixed-effect modelling programme. We searched the significant covariates for parameters, such as the dose rate for 50% inhibition of coagulation (EDR 50 ), using a stepwise forward and backward method. Monte Carlo simulation determined a required daily dose of warfarin with a target range of PT-INR (2.0-3.0 or 1.6-2.6) based on the significant covariates., Results: A total of 350 patients with 2762 PT-INR measurements were enrolled (estimated glomerular filtration rate [eGFR]: 47.5 [range: 2.6-199.0] mL/min/1.73 m 2 ). The final kinetic-pharmacodynamic model showed that the EDR 50 changed power functionally with body surface area, serum albumin level and eGFR. Monte Carlo simulation revealed that a lower daily dose of warfarin was required to attain the target PT-INR range as eGFR decreased., Conclusions: Model-informed precision dosing of warfarin is a valuable approach for estimating its dosage in patients with renal impairment., (© 2023 British Pharmacological Society.)

Aims: The aim of this study was to investigate the association between VKORC1 and CYP2C9 genes polymorphisms and the maintenance dose of warfarin in Peruvian patients., Methods: An observational study was conducted on outpatients from the Hospital Grau ESSALUD in Lima, Peru. The participants were selected using nonprobabilistic convenience sampling. Inclusion criteria required patients to have been on anticoagulation therapy for >3 months, maintain stable doses of warfarin (consistent dose for at least 3 outpatient visits), and maintain an international normalized ratio within the therapeutic range of 2.5-3.5. DNA samples were obtained from peripheral blood for gene analysis., Results: Seventy patients (mean age of 69.6 ± 13.4 years, 45.7% female) were included in the study. The average weekly warfarin dose was 31.6 ± 15.2 mg. The genotypic frequencies of VKORC1 were as follows: 7.1% (95% confidence interval, 2.4-15.9) for AA; 44.3% (32.4-56.7) for GA; and 48.6% (36.4-60.8) for GG. No deviation from the Hardy-Weinberg equilibrium was observed in the variants studied (P = .56). The mean weekly warfarin doses for AA, GA and GG genotypes were 16.5 ± 2.9, 26.5 ± 9.5 and 37.9 ± 17.1 mg, respectively (P < .001). The genotypic frequencies of CYP2C9 were as follows: 82.8% (72.0-90.8) for CC (*1/*1); 4.3% (1.0-12.0) for CT (*1/*2); and 12.9% (6.1-23.0) for TT (*2/*2). We did not find a significant association between the CYP2C9 gene polymorphism and the dose of warfarin., Conclusions: The AA genotype of the VKORC1 gene was associated with a lower maintenance dose of warfarin in Peruvian patients., (© 2023 British Pharmacological Society.)

Introduction: Guidelines recommend "rapid" and "urgent" reversal of anticoagulation for warfarin-associated intracranial hemorrhage (ICH) treatment; however, they do not specify goals for time-to-administration. There are limited studies evaluating time to reversal, or international normalized ratio (INR) correction, on hematoma expansion and outcomes in intervals of <4 h. The purpose of this study was to evaluate the association of 4-factor prothrombin concentrate (4F-PCC) time-to-administration on rates of achieving effective hemostasis, determined by hematoma expansion, for treatment of warfarin-associated ICH., Methods: This was a retrospective, observational, single center study performed at a large community teaching hospital. Patients were stratified into three groups based on time of CT diagnosis of ICH to administration of 4F-PCC: <45 min, 45-90 min, and >90 min. The primary outcome was rates of achieving effective hemostasis in each group defined as a ≤20% increase in hematoma volume as estimated by a radiologist., Results: A total of 227 patients were screened for inclusion with ultimately 39 being included. Baseline characteristics were similar between groups. The primary outcome was not significantly different among groups stratified by time to 4F-PCC administration of <45 min, 45-90 min, and >90 min (85.7% vs 73.3% vs 90%, p value 0.514). There was no difference among secondary outcomes between groups including in-hospital mortality, hospital length of stay (LOS), and intensive care unit LOS., Conclusion: There was no association with time-to-administration of 4F-PCC on rates of hemostasis achievement, defined as hematoma expansion of ≤20%, identified in this study., Competing Interests: Declaration of Competing Interest The authors of this study have no financial conflicts of interest nor disclosures to report., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Background: High altitude environment affects the pharmacokinetic (PK) parameters of drugs and the PK parameters are an important theoretical basis for guiding the rational clinical use of drugs. Warfarin is an oral anticoagulant of the coumarin class commonly used in clinical practice, but it has a narrow therapeutic window and wide individual variation. However, the effect of high altitude environment on PK and pharmacodynamic (PD) of warfarin is unclear., Objective: The objective of this study is to investigate the effect of a high altitude environment on PK and PD of warfarin in rats., Method: Rats were randomly divided into plain group and high altitude group and blood samples were collected through the orbital venous plexus after administration of 2 mg/kg warfarin. Warfarin concentrations in plasma samples were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and PK parameters were calculated by the non-compartment model using WinNonlin 8.1 software. Meanwhile, the expression of PXR, P-gp and CYP2C9 in liver tissues was also determined by western blotting. The effect of high altitude environment on PD of warfarin was explored by measuring activated partial thromboplastin time (APTT) and prothrombin time (PT) values and then calculated international normalized ratio (INR) values based on PT., Results: Significant changes in PK behaviors and PD of warfarin in high altitude-rats were observed. Compared with the plain-rats, the peak concentration (C max ) and the area under the plasma concentration-time curve (AUC) increased significantly by 50.9% and 107.46%, respectively. At the same time, high altitude environment significantly inhibited the expression of PXR, P-gp and CYP2C9 in liver tissues. The results of the PD study showed that high altitude environments significantly prolonged PT, APTT and INR values., Conclusion: High altitude environment inhibited the metabolism and increased the absorption of warfarin in rats and increased the effect of anticoagulant effect, suggesting that the optimal dose of warfarin for patients at high altitude should be reassessed., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Warfarin patient self-management (PSM) is when a patient independently manages their warfarin therapy using a decision-support tool provided by their anticoagulation provider. Clinical trials of PSM, conducted predominantly in Europe, have consistently demonstrated superior efficacy without compromising safety. However, the evidence-based practice of PSM is rarely utilized in the United States (U.S.). We describe initiatives completed to implement a successful PSM program among experienced warfarin-taking patients in a U.S. academic health system by overcoming perceived barriers. The results showed PSM resulted in similar or improved INR control, and an estimated 68% reduction in pharmacist workload., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Background Warfarin has a narrow therapeutic index and needs regular international normalized ratio monitoring and dose adjustment. Poor quality of warfarin dosing can lead to an increased risk of adverse events. Objective To find out the overall quality of the international normalized ratio expressed in terms of time in therapeutic range and adverse outcomes associated with the use of warfarin. Method A descriptive cross-sectional study among 150 patients attending a tertiary care center receiving warfarin therapy from December 2022 to June 2023. Patients receiving warfarin at least for 6 months and with at least three international normalized ratio values were enrolled. Indications, average daily dosing, international normalized ratio, and adverse effects were recorded using convenient sampling. Data were analyzed by using SPSS, version 20. Result The mean age was 46.41±13.96 years. Indications for warfarin were valvular and nonvalvular atrial fibrillation in 104 (69.33%), deep vein thrombosis 21 (14%), and pulmonary embolism 6 (4%). The majority of patients 100 (66.6%) received 5 to 10mg of warfarin per day. The mean duration of warfarin use was 18.11±21.93 months. The mean time in the therapeutic range (%) was 62.43±27.52. Sixty patients (40%) had time in the therapeutic range below 60%. Among the adverse effects, minor bleeding was present in 25 (16.66%). The ischemic event was present in 7 (4.7%). Conclusion Our patients had lower time in the therapeutic range than recommended in the guidelines. They had a longer time in the sub-therapeutic range.

Warfarin has been the most extensively used oral anticoagulant (OAC) in medical settings for over 60 years. Its uses, potential adverse effects, and methods for reversing its effects have been firmly established, rendering it a routine medication in medical settings where most professionals feel at ease employing it. Compared to other vitamin K antagonists (VKAs), such as acenocoumarol, warfarin offers benefits like diminished prothrombin time (PT) assays leading to enhanced oral anticoagulation. Observations over the past few years have seen the inclusion of novel/direct OACs (NOACs/DOACs) in the anticoagulant armamentarium. Although DOACs have several advantages, warfarin still has an important role in subsets of patients where DOACs are contraindicated, not well-tolerated, or cannot afford DOACs due to higher costs. Moreover, there are patient profiles where warfarin is still considered a superior choice compared to DOACs, such as age group of >75 years, kidney failure with creatinine clearance (CrCl) below 30 mL/minute, and prosthetic mechanical valve replacement. Precise management of the international normalized ratio (INR) is crucial for the effectiveness of warfarin treatment. INR monitoring is the major concern in the Indian context due to the lack of laboratories for standardized measurement. Adopting strategies such as point-of-care INR monitoring devices and anticoagulation clinics can help to improve clinical outcomes with warfarin therapy. The present review provides a critical overview of the role of warfarin therapy in the current OAC arsenal and strategies for improving therapeutic control and patient adherence. How to cite this article : Nair T. Critical Appraisal on the Role of Warfarin in the Current Era. J Assoc Physicians India 2023;71(10):31-36., (© Journal of the Association of Physicians of India 2023.)

Background: Essential to the coagulation pathway, vitamin K (phytonadione) is used to correct clotting factor deficiencies and for reversal of warfarin-induced bleeding. In practice, high-dose intravenous (IV) vitamin K is often used, despite limited evidence supporting repeated dosing., Objective: This study sought to characterize differences in responders and nonresponders to high-dose vitamin K to guide dosing strategies., Methods: This was a case-control study of hospitalized adults who received vitamin K 10 mg IV daily for 3 days. Cases were represented by patients who responded to the first dose of IV vitamin K and controls were nonresponders. The primary outcome was change in international normalized ratio (INR) over time with subsequent vitamin K doses. Secondary outcomes included factors associated with response to vitamin K and incidence of safety events. The Cleveland Clinic Institutional Review Board approved this study., Results: There were 497 patients included, and 182 were responders. Most patients had underlying cirrhosis (91.5%). In responders, the INR decreased from 1.89 at baseline (95% CI = [1.74-2.04]) to 1.40 on day 3 (95% CI = [1.30-1.50]). In nonresponders, the INR decreased from 1.97 (95% CI = [1.83-2.13]) to 1.85 ([1.72-1.99]). Factors associated with response included lower body weight, absence of cirrhosis, and lower bilirubin. There was a low incidence of safety events observed., Conclusions: In this study of mainly patients with cirrhosis, the overall adjusted decrease in INR over 3 days was 0.3, which may have minimal clinical impact. Additional studies are needed to identify populations who may benefit from repeated daily doses of high-dose IV vitamin K.

Background: Prothrombinex-VF is being increasingly used as an off-label therapy to correct non-warfarin-related elevations in international normalised ratio (INR) in the critically ill. Currently there are no dosing guidelines for such use., Aims: To validate a prediction equation, embedded in a smartphone application (app), to guide dosing of Prothrombinex-VF in critically ill patients., Methods: A prospective pilot cohort study of critically ill adult patients with elevated INRs who were treated with Prothrombinex-VF. The main outcome measured was INR following Prothrombinex-VF administration., Results: Of the 31 patients included, five (16%) were taking warfarin prior to admission and 14 (45%) had chronic liver disease. There was a significant decrease in INR after Prothrombinex-VF treatment (P < 0.001) and a significant correlation between the app's predicted INRs and the measured INRs (r = 0.63 and P < 0.001). The app's predicted INRs were less accurate for patients with chronic liver disease than for those without. Overall, the app's recommendations achieved an INR either similar to (29.6%) or better than (55.6%) what would have been achieved had the warfarin reversal guidelines been applied to dose the Prothrombinex-VF., Conclusion: The app appeared to be reasonably accurate at predicting normalisation of elevated INRs after administration of Prothrombinex-VF, especially among patients without liver disease. Its dosing recommendations were similar to or possibly better than preexisting warfarin reversal guidelines in over 85% of the situations analysed, if we assume a higher dose of Prothrombinex-VF would achieve a greater reduction in INR than a lower dose., (© 2022 Royal Australasian College of Physicians.)

Aims: Dicloxacillin is used to treat staphylococcal infections and we have previously shown that dicloxacillin is an inducer of cytochrome P450 enzymes (CYPs). Here, we employed a translational approach to investigate the effect of a treatment with dicloxacillin on warfarin efficacy in Danish registries. Furthermore, we assessed dicloxacillin as an inducer of CYPs in vitro., Methods: We conducted a register-based study and analysed international normalized ratio (INR) levels in chronic warfarin users before and after short- and long-term use of dicloxacillin (n = 1023) and flucloxacillin (n = 123). Induction of CYPs were investigated in a novel liver model of 3D spheroid primary human hepatocytes at the level of mRNA, and protein and enzyme activity., Results: Short- and long-term dicloxacillin treatments decreased INR levels by -0.65 (95% confidence interval [CI]: -0.57 to -0.74) and -0.76 (95% CI: -0.50 to -1.02), respectively. More than 90% of individuals experienced subtherapeutic INR levels (below 2) after long-term dicloxacillin treatment. Flucloxacillin decreased INR levels by -0.37 (95% CI: -0.14 to -0.60). In 3D spheroid primary human hepatocytes, the maximal induction of CYP3A4 mRNA, protein and enzyme activity by dicloxacillin were 4.9-, 2.9- and 2.4-fold, respectively. Dicloxacillin also induced CYP2C9 mRNA by 1.7-fold., Conclusion: Dicloxacillin induces CYPs and reduces the clinical efficacy of warfarin in patients. This effect is substantially exacerbated during long-term treatment with dicloxacillin. The in vitro results corroborated this drug-drug interaction and correlated to the clinical findings. Caution is warranted for warfarin patients that initiate dicloxacillin or flucloxacillin, especially for a long-term treatment of endocarditis., (© 2023 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Background: Point-of-care testing (POCT) coagulometers are increasingly used for monitoring warfarin therapy. However, in high international normalized ratio (INR) ranges, significant discrepancy in the INR between POCT and conventional laboratory tests occurs. We compared the INR of POCT (CoaguChek XS Plus; Roche Diagnostics, Mannheim, Germany) with that of a conventional laboratory test (ACL TOP 750; Instrumentation Laboratory SpA, Milan, Italy) and explored possible reasons for discrepancy., Methods: Paired POCT and conventional laboratory test INRs were analyzed in 400 samples from 126 patients undergoing warfarin therapy after cardiac surgery. Coagulation factor and thrombin generation tests were compared using the Mann-Whitney U test. Correlations between coagulation factors and INRs were determined using Pearson correlation coefficients., Results: The mean difference in the INR between the tests increased at high INR ranges. Endogenous thrombin potential levels were decreased at INR <2.0 for CoaguChek XS Plus and 2.0< INR <3.0 for ACL TOP 750 compared with those at INR <2.0 for both tests, indicating a better performance of ACL TOP 750 in assessing thrombin changes. The correlation coefficients of coagulation factors were stronger for ACL TOP 750 INR than for CoaguChek XS Plus INR. Vitamin K-dependent coagulation factors were found to contribute to the INR discrepancy., Conclusions: Decreases in vitamin K-dependent coagulation and anticoagulation factors can explain the significant discrepancy between the two tests in high INR ranges. Since conventional laboratory test INR values are more reliable than POCT INR values, a confirmatory conventional laboratory test is required for high INR ranges.

Purpose: The anticoagulation activity of warfarin in populations with CYP2C9, VKORC1, and CYP4F2 variants differs between individuals and is correlated with poor international normalized ratio (INR) control. Pharmacogenetics-guided warfarin dosing has been successfully developed for patients with genetic variations in recent years. However, few real-world data have been used to investigate the INR and warfarin dosage and the time to target INR. This study examined the largest collection of genetic and clinical real-world data related to warfarin to provide further evidence supporting the benefits of pharmacogenetics in clinical outcomes., Methods: We retrieved a total of 69,610 INR-warfarin records after the index date from 2,613 patients in the China Medical University Hospital database between January 2003 and December 2019. Each INR reading was obtained from the latest laboratory data after the hospital visit date. Patients with a history of malignant neoplasms or pregnancy before the index date were excluded, as were patients without data on INR measurements after the fifth day of prescription, genetic information, or gender variables. The primary outcomes were the INR and warfarin dosage during days 7, 14, 28, 56, and 84 after prescription. The secondary outcome was the time required to reach the INR ranges of 1.5 to 3.0 and >4.0., Findings: A total of 59,643 INR-warfarin records from 2188 patients were retrieved. The average INR was higher for homozygous carriers of the minor allele at CYP2C9 and VKORC1 during the first 7 days (1.83 [1.03] [CYP2C9*1] and 2.46 [1.44] [CYP2C9*3], P < 0.001; 1.39 [0.36] [rs9923231 G/G], 1.55 [0.79] [rs9923231 G/A], and 1.96 [1.13] [rs9923231 A/A], P < 0.001) than for the wild-type allele. These patients with variants required lower warfarin doses than those with the wild-type allele during the first 28 days. CYP4F2 variant patients seemed to require higher doses of warfarin than those in the wild-type group; however, no significant difference in the average INR was observed (1.95 [1.14] [homozygous V433 carriers], 1.78 [0.98] [heterozygous V433M carriers], and 1.66 [0.91] [homozygous M433 carriers], P = 0.016)., Implications: Our study indicates that genetic variants in the Han population may enhance warfarin responsiveness, which holds clinical relevance. An increased warfarin dosage was not linked to a shorter time to therapeutic INR between CYP4F2 variant patients and those with a wild-type allele. Assessing CYP2C9 and VKORC1 genetic polymorphisms before initiating warfarin treatment in real-world practice is essential for potentially vulnerable patients and is likely to optimize therapeutic dosing., Competing Interests: Declaration of Competing Interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest., (Copyright © 2023. Published by Elsevier Inc.)

Background: Numerous genotype-guided warfarin dosing algorithms have been developed to individualize warfarin doses, but they can only explain 47-52% of the variability., Aim: This study aimed to develop new warfarin algorithms suitable to predict the stable warfarin dose for the Chinese population and to compare their prediction performance with those of the most commonly used algorithms., Method: Multiple linear regression analysis with the warfarin optimal dose (WOD), logarithm (log) WOD, 1/WOD, and [Formula: see text], respectively, as the dependent variables were performed to deduce a new warfarin algorithm (NEW-Warfarin). WOD was the stable dose that maintained the international normalized ratio (INR) within the target range (2.0-3.0). Three major genotype-guided warfarin dosing algorithms were selected and compared against NEW-Warfarin predictive performance using the mean absolute error (MAE). Furthermore, patients were divided into five groups according to warfarin indications [atrial fibrillation (AF), pulmonary embolism (PE), cardiac-related disease (CRD), deep vein thrombosis (DVT), and other diseases (OD)]. Multiple linear regression analyses were also performed for each group., Results: The regression equation with [Formula: see text] as the dependent variable had the highest coefficient of determination (R 2  = 0.489). The NEW-Warfarin had the best predictive accuracy compared to the three algorithms selected. Group analysis, according to indications, showed that the R 2 of the five groups were PE (0.902) > DVT (0.608) > CRD (0.569) > OD (0.436) > AF (0.424)., Conclusion: Dosing algorithms based on warfarin indications are more suitable for predicting warfarin doses. Our research provides a novel strategy to develop indication-specific warfarin dosing algorithms to improve the efficacy and safety of warfarin prescribing., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Objective: To study the profile, clinical presentation and outcome of hospital stay among patients admitted with warfarin toxicity at the Jigme Dorji Wangchuck National Referral Hospital, Bhutan. This was a cross-sectional study with a review of hospital records of patients admitted between 01 and 2018 and 30 June 2020., Results: There were 22 admissions due to warfarin toxicity. The mean age of patients was 55.9 (± SD 20.2) years, the median duration of warfarin therapy was 30 months (IQR 4.8, 69 months). The indications for warfarin were atrial fibrillation (9, 40.9%), mechanical heart valves (6, 27.3%), deep vein thrombosis (6, 27.3%) and pulmonary thromboembolism (1, 4.5%). The mean of dosage of warfarin was 4.3 (± 2.6) mg and the cumulative dosage in the week prior to admission was 30.9 (± 18.6) mg. The mean of INR at presentation was 7.7 (± 4.3) with the maximum noted at 20. The patients presented with gastrointestinal bleeding, muscle haematomas, epistaxis and oral cavity bleeding. There was no mortality related to warfarin toxicity. The reasons for warfarin toxicity included patient dosing error and drug interactions. Warfarin therapy requires appropriate patient education, adequate facilities for follow-up and avoidance of warfarin wherever possible in clinical settings., (© 2023. The Author(s).)