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Background: Home-based hospital services are becoming increasingly popular, and the addition of remote outpatient appointments after kidney transplantation facilitates more practical and closer follow-up. In this context, finger-prick self-sampling is an important aspect of monitoring of immunosuppressants and biomarkers. Nevertheless, several issues must be addressed to ensure the feasibility and quality when implementing microsampling in clinical practice. We summarize our experiences and opinions in this field., Methods: This article is based on the authors' experience regarding the laboratory and clinical implementation of finger-prick self-sampling in kidney transplant recipients. The referenced literature is related to the authors' knowledge in this field., Results: We present considerations for the selection of relevant analytes, key characteristics of selected volumetric sampling tools (Mitra and Capitainer), and the associated sampling pitfalls. In addition, we address the requirements for patients performing finger-prick sampling, appropriate design of methods and workflow, critical points for validation, and aspects related to logistics and digital solutions., Conclusions: Volumetric finger-prick self-sampling is suitable for monitoring immunosuppressants and certain biomarkers that are relevant to outpatient follow-up after kidney transplantation. We believe that a carefully designed system for the entire workflow, including patient training, will be beneficial in enabling a safe experience for transplant recipients, as well as ensuring overall efficiency and adequate quality. In the future, a combination of immunosuppressants with a wide range of biomarkers has significant potential for use in at-home self-sampling after kidney transplantation., Competing Interests: The authors declare no conflict of interest., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Aims: Finger-prick sampling has emerged as an attractive tool for therapeutic drug monitoring and associated diagnostics. We aimed to validate the clinical performance of using two volumetric devices (Capitainer® qDBS and Mitra®) for monitoring tacrolimus, creatinine and haemoglobin in kidney transplant (KTx) recipients. Secondarily, we evaluated potential differences between finger-prick sampling performed by healthcare professionals vs. self-sampling, and differences between the two devices., Methods: We compared finger-prick and venous sampling in three settings: microsampling performed by healthcare personnel, self-sampling under supervision, unsupervised self-sampling. The finger-prick samples were analysed with adapted methods and results compared to routine method analysis of the venous blood samples., Results: Twenty-five KTx recipients completed the main study and 12 KTx recipients completed a post hoc validation study. For tacrolimus measurements and predicted area under the curve, the proportions within ±20% difference were 79%-96% for Capitainer and 77%-95% for Mitra. For creatinine and haemoglobin, the proportions within ±15% were 92%-100% and 93%-100% for Capitainer and 79%-96% and 67%-92% for Mitra, respectively. Comparing sampling situations, the success rate was consistent for Capitainer (92%-96%), whereas Mitra showed 72%-88% and 52%-72% success rates with samples collected by healthcare personnel and the patients themselves., Conclusions: Capitainer and Mitra are technically feasible for measuring tacrolimus, creatinine and haemoglobin. In the context of self-sampling, Capitainer maintained consistent sampling success and analytical quality. Implementing volumetric finger-prick self-sampling for the monitoring of tacrolimus, creatinine and haemoglobin may simplify and improve the follow-up of KTx recipients., (© 2023 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Background: Prednisolone (PL) is a standard component of most immunosuppressive protocols after solid organ transplantation (Tx). Adverse effects are frequent and well known. The aim of this study was to characterize the pharmacokinetics (PKs) of PL and prednisone (PN), including cortisol (CL) and cortisone (CN) profiles, after PL treatment in renal Tx recipients in the early post-Tx phase., Methods: This single-center, prospective, observational study included stable renal Tx recipients, >18 years of age, and in the early postengraftment phase. Blood samples were obtained predose and during a 24-hour dose interval [n = 26 samples per area under the curve (AUC0-24)], within the first 8 weeks post-Tx. PL, PN, CL, and CN concentrations were measured using high-performance liquid chromatography-tandem mass spectrometry., Results: In renal Tx recipients (n = 28), our results indicated a relatively high PL exposure [median, range AUC0-24 = 3821 (2232-5382) mcg h/L], paralleled by strong suppression of endogenous CL profile, demonstrated by a low CL evening-to-morning ratio [median, range 11 (3-47)%]. A negative correlation (r = -0.83) between PL AUC0-24 and morning CL levels was observed. The best single PK variable to predict PL AUC0-24 was PL C6 (r2 = 0.82). An algorithm based on 3 PK sampling time points: trough, 2, and 4 hours after PL dosing, predicted PL AUC0-24 with a low percentage prediction error (PPE = 5.2 ± 1.5%) and a good correlation of determination (r2 = 0.91). PL AUC0-24 varied 3-fold among study participants, whereas CL AUC0-24 varied by 18-fold., Conclusions: The large interindividual variability in both PL exposure and suppression of endogenous CL implies a possible role for therapeutic drug monitoring. An abbreviated profile within the first 4 hours after PL dosing provides a good prediction of PL exposure in renal Tx recipients. The strong negative correlation between PL AUC0-24 and morning CL levels suggests a possible surrogate marker for drug exposure for further evaluation., Competing Interests: The authors declare no conflict of interest., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

Therapeutic drug monitoring (TDM) is mandatory for the immunosuppressive drug tacrolimus (Tac). For clinical applicability, TDM is performed using morning trough concentrations. With recent developments making tacrolimus concentration determination possible in capillary microsamples and Bayesian estimator predicted area under the concentration curve (AUC), AUC-guided TDM may now be clinically applicable. Tac circadian variation has, however, been reported, with lower systemic exposure following the evening dose. The aim of the present study was to investigate tacrolimus pharmacokinetic (PK) after morning and evening administrations of twice-daily tacrolimus in a real-life setting without restrictions regarding food and concomitant drug timing. Two 12 hour tacrolimus investigations were performed; after the morning dose and the following evening dose, respectively, in 31 renal transplant recipients early after transplantation both in a fasting-state and under real-life nonfasting conditions (14 patients repeated the investigation). We observed circadian variation under fasting-conditions: 45% higher peak-concentration and 20% higher AUC following the morning dose. In the real-life nonfasting setting, the PK-profiles were flat but comparable after the morning and evening doses, showing slower absorption rate and lower AUC compared with the fasting-state. Limited sampling strategies using concentrations at 0, 1, and 3 hours predicted AUC after fasting morning administration, and samples obtained at 1, 3, and 6 hours predicted AUC for the other conditions (evening and real-life nonfasting). In conclusion, circadian variation of tacrolimus is present when performed in patients who are in the fasting-state, whereas flatter PK-profiles and no circadian variation was present in a real-life, nonfasting setting., (© 2020 The Authors. Clinical and Translational Science published by Wiley Periodicals LLC on behalf of the American Society for Clinical Pharmacology and Therapeutics.)

Aims: To explore the pharmacodynamics of mycophenolic acid (MPA) through inosine monophosphate dehydrogenase (IMPDH) capacity measurement and purine levels in peripheral blood mononuclear cells (PBMC) longitudinally during the first year after renal transplantation (TX)., Methods: PBMC were isolated from renal recipients 0-4 days prior to and 6-9 days, 5-7 weeks and 1 year after TX (before and 1.5 hours after dose). IMPDH capacity and purine (guanine and adenine) levels were measured in stimulated and nonstimulated PBMC., Results: Twenty-nine patients completed the follow-up period, of whom 24 received MPA. In stimulated PBMC, the IMPDH capacity (pmol 10 -6 cells min -1 ) was median (interquartile range) 127 (95.8-147) before TX and thereafter 44.9 (19.2-93.2) predose and 12.1 (4.64-23.6) 1.5 hours postdose across study days after TX. The corresponding IMPDH capacity in nonstimulated PBMC was 5.71 (3.79-6.93), 3.35 (2.31-5.62) and 2.71 (1.38-4.08), respectively. Predose IMPDH capacity in nonstimulated PBMC increased with time, reaching pre-TX values at 1 year. In stimulated PBMC, both purines were reduced before (median 39% reduction across days after TX) and after (69% reduction) dose compared to before TX. No alteration in the purine levels was observed in nonstimulated PBMC. Patients needing dose reductions during the first year had lower pre-dose IMPDH capacity in nonstimulated PBMC (1.87 vs 3.00 pmol 10 -6 cells min -1 , P = .049) at 6-9 days., Conclusion: The inhibitory effect of MPA was stronger in stimulated PBMC. Nonstimulated PBMC became less sensitive to MPA during the first year after TX. Early IMPDH capacity appeared to be predictive of dose reductions., (© 2020 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Purpose: Until recently, it has been believed that donating a kidney not represents any risk for development of cardiovascular disease. However, a recent Norwegian epidemiological study suggests that kidney donors have an increased long-term risk of cardiovascular mortality. The pathophysiological mechanisms linking reduced kidney function to cardiovascular disease are not known. Living kidney donors are screened for cardiovascular morbidity before unilateral nephrectomy, and are left with mildly reduced glomerular filtration rate (GFR) after donation. Therefore, they represent an unique model for investigating the pathogenesis linking reduced GFR to cardiovascular disease and cardiovascular remodelling. We present the study design of Cardiovascular rEmodelling in living kidNey donorS with reduced glomerular filtration rate (CENS), which is an investigator-initiated prospective observational study on living kidney donors. The hypothesis is that living kidney donors develop cardiovascular remodelling due to a reduction of GFR. Materials and methods: 60 living kidney donors and 60 age and sex matched healthy controls will be recruited. The controls will be evaluated to fulfil the Norwegian transplantation protocol for living kidney donors. Investigations will be performed at baseline and after 1, 3, 6 and 10 years in both groups. The investigations include cardiac magnetic resonance imaging, echocardiography, bone density scan, flow mediated dilatation, laser Doppler flowmetry, nailfold capillaroscopy, office blood pressure, 24-h ambulatory blood pressure, heart rate variability and investigation of microbiota and biomarkers for inflammation, cardiovascular risk and the calcium-phosphate metabolism. Conclusions: The present study seeks to provide new insight in the pathophysiological mechanisms linking reduced kidney function to cardiovascular disease. In addition, we aim to enlighten predictors of adverse cardiovascular outcome in living kidney donors. The study is registered at Clinical-Trials.gov (identifier: NCT03729557).

Marine n-3 fatty acids (FAs) may exert beneficial effects on inflammation, fibrosis, and endothelial function, which could preserve renal graft function. In this randomized controlled trial, 132 Norwegian renal transplant recipients received either 2.6 g of marine n-3 FAs or olive oil (control) daily for 44 weeks, in addition to standard care. Thirty patients did not complete the trial. The primary endpoint was change (Δ) in measured glomerular filtration rate (mGFR) during follow-up. We found no significant difference in Δ mGFR between the marine n-3 FA group and controls (6.7 vs 3.8 mL/min per 1.73 m 2 , P = .15). Significant beneficial effects from marine n-3 FA supplementation were, however, seen in secondary endpoints plasma triglycerides, plasma high-sensitivity C-reactive protein, and brachial artery flow-mediated dilation. In the per-protocol population, the renal graft indices percent interstitial fibrosis and Chronic Allograft Damage Index also were significantly lower in the marine n-3 FA group. The cumulative incidence of adverse events did not differ between the marine n-3 FA group (n = 218) and controls (n = 240). In conclusion, marine FA supplementation did not improve renal function compared with controls, but was safe, lowered plasma triglyceride and high-sensitivity C-reactive protein levels, and improved endothelial function (Clinical.Trials.gov identifier NCT01744067)., (© 2018 The American Society of Transplantation and the American Society of Transplant Surgeons.)

Introduction: Tacrolimus (TAC) is an immunosuppressive drug used after organ transplantation. Dosing is adjusted using whole blood (WB-TAC) measurements. Patients within the therapeutic WB-TAC window still experience rejections and adverse effects. Alternative monitoring methods are therefore warranted. The authors developed a method for measuring TAC in peripheral blood mononuclear cell (PBMC) isolates (PBMC-TAC) and performed a pharmacokinetic study in a cohort of kidney transplant patients during the first year after transplantation., Methods: PBMCs were isolated from whole blood by gradient centrifugation. After methanol-based extraction, liquid chromatography with tandem mass spectrometry was used to determine TAC in the extract. PBMC-TAC was normalized to the number of cells and alternatively to the protein amount in cells. Predose and postdose (1.5 hours) samples from kidney transplant patients were collected at 1 week, 6 weeks, and 1 year after transplantation. WB-TAC was measured using immunoassay., Results: The PBMC-TAC assay fulfilled the validation criteria of the European Medicines Agency guidelines. Twenty-nine patients completed the study. Predose PBMC-TAC was (median) 23 (1 week), 33 (6 weeks), and 27 pg/10 cells (1 year). Postdose PBMC-TAC was 44, 30, and 27 pg/10 cells at 1 week, 6 weeks, and 1 year after transplantation, respectively. Predose WB-TAC (median) was 5.0, 6.0, and 5.4 mcg/L, and postdose WB-TAC was 10.5, 8.3, and 9.1 mcg/L, respectively, at 1 week, 6 weeks, and 1 year after transplantation. Whole blood and PBMC-TAC correlated at all timepoints (rho 0.40-0.82, P < 0.05) except before dosage at 6 weeks. PBMC-TAC normalized to the number of cells, and the amount of protein was modestly correlated (rho 0.36-0.81, P < 0.056)., Conclusions: The correlation between WB-TAC and PBMC-TAC is modest during the first-year posttransplantation. Normalization of PBMC-TAC to cells or protein may yield different results. PBMC-TAC is increased 1.5 hours after dose at 1 week after transplantation, but not after 6 weeks or 1 year, indicating altered distribution kinetics.

Several equations have been developed for estimated glomerular filtration rate (eGFR) in patients with chronic kidney disease (CKD), but none were developed based on data from elderly kidney transplant recipients (KTR). The primary aim of this study was to evaluate different creatinine-based equations in stable elderly KTR. A national cross-sectional study was performed using data from 263 consecutive kidney transplant recipients 60 years or older who performed a routine GFR measurement one year after engraftment. GFR was measured by iohexol clearance calculation based on two samples. eGFR was calculated from a range of different creatinine-based equations using information obtained at the time of GFR measurement. Bias, precision, and accuracy were evaluated for each equation. All equations apart from Nankivell had accuracy (P30) > 80%. The BIS1, FAS, LMR CR , and Cockcroft & Gault equations in recipients older than 70 years and the FAS, LMR CR , and MDRD in recipients 60-69 years old had nonsignificant bias. The CKD-EPI had significant bias in both groups. If one should choose a single equation for follow-up of individual CKD progression in all recipients ≥ 60 years, the FAS or LMR CR equations are probably the best alternatives., (© 2018 Steunstichting ESOT.)

Aims: Despite pharmacokinetic monitoring of calcineurin inhibitors, the long-term outcome after transplantation (Tx) is still hampered by the side effects of these drugs. The aim of the present study was to characterize nuclear factor of activated T cells (NFAT)-regulated gene expression as a potential pharmacodynamic biomarker for further individualization of tacrolimus (Tac) therapy., Methods: In 29 renal allograft recipients, samples were drawn once pre-Tx, and before and 1.5 h after Tac dosing at approximately 1 week, 6 weeks and 1 year post-Tx. Tac concentrations were measured by immunoassay, while the expression of genes encoding NFAT-regulated cytokines [interleukin 2 (IL2), interferon gamma (IFNG), colony stimulating factor 2 (CSF2)] and cytochrome P450 3A5 (CYP3A5) genotyping were determined by real-time polymerase chain reaction., Results: The cytokine response after Tac dosing varied up to 46-fold between patients and changed significantly with time post-engraftment. Tac concentrations 1.5 h postdose (C 1.5 ) >15 μg l -1 were associated with strong cytokine inhibition and residual gene expression (RGE) ≤10%, while lower Tac C 1.5 resulted in more variable responses (RGE 2.5-68.7%). Patients with ongoing subclinical acute rejection (n = 5) demonstrated limited cytokine inhibition (RGE 39.7-72.6%), while patients with polyoma virus viraemia (n = 3) had relatively strong inhibition of cytokines (RGE 2.5-32.5%). By contrast, there was no association between Tac exposure and rejection or viraemia., Conclusions: The findings of our study support the potential of NFAT-regulated gene expression measurements as a pharmacodynamic tool for additional monitoring of Tac therapy, especially in the context of overimmunosuppression and viraemia., (© 2017 The British Pharmacological Society.)

Background: Patients with high tacrolimus clearance eliminate more drug within a dose interval compared with those with low clearance. Delays in dosing time will result in transient periods of lower concentrations in high versus low clearance patients. Transient subtherapeutic tacrolimus concentrations may induce acute rejection episodes., Methods: A retrospective study in all renal transplant patients treated with tacrolimus at our center from 2009 to 2013 was conducted. The association between individually estimated tacrolimus clearance (daily tacrolimus dose [mg]/trough concentration [μg/L]) and biopsy-proven acute rejection (BPAR) the first 90 days posttransplantation was investigated., Results: In total, 638 patients treated with oral tacrolimus were included in the analysis. Eighty-five (13.3%) patients experienced BPAR. Patients were stratified into 4 groups per their estimated clearance. The patients in the high clearance group had significantly higher incidence of BPAR (20.6%) with a hazard ratio of 2.39 (95% confidence interval, 1.30-4.40) compared with the low clearance group. Clearance estimate (as a continuous variable) showed a hazard ratio of 2.25 (95% confidence interval, 1.70-2.99) after adjusting for other risk factors. There were no significant differences in neither trough concentrations the first week after transplantation nor time to target trough concentration between patients later experiencing BPAR or not., Conclusions: High estimated clearance is significantly associated with increased risk of BPAR the first 90 days posttransplantation and may predict an increased risk of rejection in the early phase after renal transplantation.

Background: Mycophenolic acid (MPA) is the active immunosuppressive substance in both mycophenolate mofetil and mycophenolate sodium, and it is widely used after organ transplantation. In women, taking MPA is teratogenic and may also influence spermatogenesis. There is a lack of knowledge regarding outcome of pregnancies fathered by men exposed to MPA., Methods: We compared outcomes in pregnancies fathered by renal transplant men per whether they had been exposed to MPA or not at time of conception. A nationwide population-based retrospective cohort study was performed. Data from the Norwegian Renal Registry with all renal transplanted men alive between January 1, 1995 and December 31, 2015 were included, and relevant outcome data were extracted from the Medical Birth Registry of Norway., Results: During the given time, 230 immunosuppressed renal transplanted men fathered 350 children (155 on MPA/195 not on MPA). There were no significant increased risks of malformation (3.9% vs. 2.6%, P = 0.49) in MPA exposed versus unexposed cohorts of children. The average dose (±SD) of mycophenolate was 1.42 ± 0.3 g/day and the individual median MPA trough concentration in the time period of anticipated conception and pregnancy was 2.8 ± 1.6 mg/L. Birth weight was similar in exposed and unexposed cohorts of children; 3381 ± 681 g vs. 3429 ± 714 g (P = 0.53)., Conclusions: Paternal exposure to MPA did not increase the risk of adverse birth outcomes in children fathered by male kidney transplanted patients. These results are reassuring and support the continuation of paternal MPA treatment before, during, and after conception.

Aims: Tacrolimus is a cornerstone in modern immunosuppressive therapy after kidney transplantation. Tacrolimus dosing is challenged by considerable pharmacokinetic variability, both between patients and over time after transplantation, partly due to variability in cytochrome P450 3A (CYP3A) activity. The aim of this study was to assess the value of the endogenous CYP3A marker 4β-hydroxycholesterol (4βOHC) for tacrolimus dose individualization early after kidney transplantation., Methods: Data were obtained from 79 adult kidney transplant recipients who contributed a total of 625 4βOHC measurements and 1999 tacrolimus whole blood concentrations during the first 2 months after transplantation. The relationships between 4βOHC levels and individual estimates of tacrolimus apparent plasma clearance (CL/F plasma ) at different time points after transplantation were investigated using scatterplots and population pharmacokinetic modelling., Results: There was no significant correlation between pre-transplant 4βOHC levels and tacrolimus CL/F plasma the first week (r = 0.19 [95% CI -0.03-0.40]) or between 4βOHC and tacrolimus CL/F plasma 1 week (r = 0.20 [-0.11-0.47]), 4 weeks (r = 0.21 [-0.07-0.46]) or 2 months (r = 0.24 [-0.03-0.48]) after transplantation (P ≥ 0.06). In the population analysis, time-varying 4βOHC was not a statistically significant covariate on tacrolimus CL/F plasma , neither in terms of absolute values (P = 0.11) nor in terms of changes from baseline (P = 0.17). 4βOHC values increased between 1 week and 2 months after transplantation (median change +57% [IQR +22-83%], P < 0.001), indicating increasing CYP3A activity. Contradictorily, tacrolimus CL/F plasma decreased over the same period (median change -13% [IQR -3 to -26%], P < 0.001)., Conclusions: 4βOHC does not appear to have a clinical potential to improve individualization of tacrolimus doses early after kidney transplantation., (© 2017 The British Pharmacological Society.)

Aim: Optimal tacrolimus exposure in transplant recipients is not well established. The results from the Symphony study indicated that low-target tacrolimus (trough concentrations 3-7 µg/L) in de novo standard risk renal transplant recipients should be appropriate. The aim of this study was to evaluate real-life outcomes when applying a similar strategy in a clinical setting., Methods: A single-centre analysis was conducted in standard risk renal transplant recipients receiving low-target tacrolimus, mycophenolate mofetil, glucocorticoids and basiliximab induction. One-year estimated glomerular filtration rate (eGFR, Cockcroft-Gault), one-year biopsy-proven acute rejection rate and graft- and patient survival up to 3 years post-transplant were compared with the outcomes in the Symphony study., Results: From 1 January 2009 to 31 March 2013, we included 406 patients. One year after transplantation, the mean ± SD eGFR was 76.8 ± 28.3 mL/min (Symphony: 65.4 ± 27.0 mL/min, P < 0.001). Biopsy-proven acute rejections were seen in 14.5% of the patients (Symphony: 12.3%, P = 0.35). Kaplan-Meier estimates [95% confidence interval] of three-year death-censored graft- and patient survival were 96.6% [94.2-99.0%] (Symphony: 93%) and 95.0% [92.6-97.3%] (Symphony: 95%), respectively., Conclusion: Low-target tacrolimus-based immunosuppression is safe and effective also in a standard clinical setting in de novo standard risk renal transplant recipients., (© 2016 Asian Pacific Society of Nephrology.)

Belatacept is a novel immunosuppressive drug that inhibits the co-stimulatory signal required for T-cell activation and has been approved for the prevention of acute rejection after kidney transplantation. In this article, the need for and possibility of therapeutic drug monitoring (TDM) of belatacept is reviewed. Clinical studies have defined the upper limit of the therapeutic window, but the lower limit is unknown. The pharmacokinetics and pharmacodynamics of belatacept display only limited interpatient variability but no data are available on the intrapatient variability of these parameters. Several assays to measure serum belatacept concentrations and its in vitro immunologic effects have been developed, but these are not commercially available and require validation. Importantly, pharmacodynamic assays have not been correlated with clinical outcomes (both efficacy and safety) and have only used surrogate laboratory readouts. TDM is likely to become feasible in the near future if these assays are developed further. However, because its pharmacokinetics and pharmacodynamics seem to vary little between individual patients, it may not be necessary to perform TDM for this drug. There could be a role for such an approach if one seeks to lower the belatacept doses further in an attempt to minimize adverse events. A future, prospective concentration-ranging study that defines the lower end of the belatacept therapeutic window should, however, be conducted first to provide the rationale for performing TDM of this novel immunosuppressant.

Background: Early after renal transplantation, it is often challenging to achieve and maintain tacrolimus concentrations within the target range. Computerized dose individualization using population pharmacokinetic models may be helpful. The objective of this study was to prospectively evaluate the target concentration achievement of tacrolimus using computerized dosing compared with conventional dosing performed by experienced transplant physicians., Methods: A single-center, prospective study was conducted. Renal transplant recipients were randomized to receive either computerized or conventional tacrolimus dosing during the first 8 weeks after transplantation. The median proportion of tacrolimus trough concentrations within the target range was compared between the groups. Standard risk (target, 3-7 μg/L) and high-risk (8-12 μg/L) recipients were analyzed separately., Results: Eighty renal transplant recipients were randomized, and 78 were included in the analysis (computerized dosing (n = 39): 32 standard risk/7 high-risk, conventional dosing (n = 39): 35 standard risk/4 high-risk). A total of 1711 tacrolimus whole blood concentrations were evaluated. The proportion of concentrations per patient within the target range was significantly higher with computerized dosing than with conventional dosing, both in standard risk patients (medians, 90% [95% confidence interval {95% CI}, 84-95%] vs 78% [95% CI, 76-82%], respectively, P < 0.001) and in high-risk patients (medians, 77% [95% CI, 71-80%] vs 59% [95% CI, 40-74%], respectively, P = 0.04)., Conclusions: Computerized dose individualization improves target concentration achievement of tacrolimus after renal transplantation. The computer software is applicable as a clinical dosing tool to optimize tacrolimus exposure and may potentially improve long-term outcome.

Background: Proper bioequivalence studies comparing original with generic immunosuppressive drugs in patients are limited, especially in the increasing population of elderly renal transplant recipients. We performed an open-label, single-center, prospective, randomized, cross-over study and compared steady-state pharmacokinetics (PK) of a generic tacrolimus (Tacni) formulation with the original (Prograf) in renal transplant recipients older than 60 years., Methods: Twenty-eight patients, with a median age of 69 years (range, 60 to 78), were randomized at time of transplantation to receive original or generic tacrolimus, and 25 (21 men, 4 women) provided two evaluable 12-hr PK profiles. The PK investigations were performed in a stable phase approximately 6 and 8 weeks postengraftment. After the first PK investigation, tacrolimus formulations were switched (1:1 dose ratio)., Results: Generic tacrolimus did not meet the bioequivalence criteria; the area under the curve(0-12) ratio of generic-original tacrolimus formulation was 1.17 (90% confidence interval, 1.10-1.23) and the Cmax ratio was 1.49 (90% confidence interval, 1.35-1.65). The generic formulation also showed a shorter time to C(max) (T(max)) (P=0.04). Importantly, the lack of bioequivalence was not reflected in the standard monitoring parameter, trough concentrations (P=0.80)., Conclusion: Generic tacrolimus (Tacni) was not found to be bioequivalent to the original formulation in elderly renal transplant recipients. The significantly higher systemic exposure of tacrolimus, despite similar trough concentrations, may in the long run increase the risk of adverse effects.

Aims: The aim was to develop a theory-based population pharmacokinetic model of tacrolimus in adult kidney transplant recipients and to externally evaluate this model and two previous empirical models., Methods: Data were obtained from 242 patients with 3100 tacrolimus whole blood concentrations. External evaluation was performed by examining model predictive performance using Bayesian forecasting., Results: Pharmacokinetic disposition parameters were estimated based on tacrolimus plasma concentrations, predicted from whole blood concentrations, haematocrit and literature values for tacrolimus binding to red blood cells. Disposition parameters were allometrically scaled to fat free mass. Tacrolimus whole blood clearance/bioavailability standardized to haematocrit of 45% and fat free mass of 60 kg was estimated to be 16.1 l h−1 [95% CI 12.6, 18.0 l h−1]. Tacrolimus clearance was 30% higher (95% CI 13, 46%) and bioavailability 18% lower (95% CI 2, 29%) in CYP3A5 expressers compared with non-expressers. An Emax model described decreasing tacrolimus bioavailability with increasing prednisolone dose. The theory-based model was superior to the empirical models during external evaluation displaying a median prediction error of −1.2% (95% CI −3.0, 0.1%). Based on simulation, Bayesian forecasting led to 65% (95% CI 62, 68%) of patients achieving a tacrolimus average steady-state concentration within a suggested acceptable range., Conclusion: A theory-based population pharmacokinetic model was superior to two empirical models for prediction of tacrolimus concentrations and seemed suitable for Bayesian prediction of tacrolimus doses early after kidney transplantation.

Purpose: Tacrolimus (Tac) and cyclosporine (CsA) are mainly metabolized by CYP3A4 and CYP3A5. Several studies have demonstrated an association between the CYP3A5 genotype and Tac dose requirements. Recently, CYP3A4, PPARA, and POR gene variants have been shown to influence CYP3A metabolism. The present study investigated potential associations between CYP3A5*3, CYP3A4*22, PPARA c.209- 1003G>A and c.208+3819A>G, and POR*28 alleles and dose-adjusted concentrations (C/D) of Tac and CsA in 177 renal transplant patients early post-transplant., Methods: All patients (n=177) were genotyped for CYP3A4*22, CYP3A5*3, POR*28, PPARA c.209-1003G>A, and PPARA c.208+3819A>G using real-time polymerase chain reaction (PCR) and melting curve analysis with allelespecific hybridization probes or PCR restriction fragment length polymorphisms (RFLP) methods. Drug concentrations and administered doses were retrospectively collected from patient charts at Oslo University Hospital, Rikshospitalet, Norway. One steady-state concentration was collected for each patient., Results: We confirmed a significant impact of the CYP3A5*3 allele on Tac exposure. Patients with POR*28 and PPARA variant alleles demonstrated 15 % lower (P=0.04) and 19 % higher (P=0.01) Tac C0/D respectively. CsA C2/D was 53 % higher among CYP3A4*22 carriers (P=0.03)., Conclusion: The results support the use of pre-transplant CYP3A5 genotyping to improve initial dosing of Tac, and suggest that Tac dosing may be further individualized by additional POR and PPARA genotyping. Furthermore, initial CsA dosing may be improved by pre-transplant CYP3A4*22 determination.

Purpose: To identify patient characteristics that influence tacrolimus individual dose requirement in kidney transplant recipients., Methods: Data on forty-four 12-h pharmacokinetic profiles from 29 patients and trough concentrations in 44 patients measured during the first 70 days after transplantation (1,546 tacrolimus whole blood concentrations) were analyzed. Population pharmacokinetic modeling was performed using NONMEM 7.2®., Results: Standardization of tacrolimus whole blood concentrations to a hematocrit value of 45 % improved the model fit significantly (p<0.001). Fat-free mass was the best body size metric to predict tacrolimus clearance and volume of distribution. Bioavailability was 49 % lower in expressers of cytochrome P450 3A5 (CYP3A5) than in CYP3A5 nonexpressers. Younger females (<40 years) showed a 35 % lower bioavailability than younger males. Bioavailability increased with age for both males and females towards a common value at age >55 years that was 47 % higher than the male value at age <40 years. Bioavailability was highest immediately after transplantation, decreasing steeply thereafter to reach its nadir at day 5, following which it increased during the next 55 days towards an asymptotic value that was 28 % higher than that on day 5., Conclusions: Hematocrit predicts variability in tacrolimus whole blood concentrations but is not expected to influence unbound (therapeutically active) concentrations. Fat-free mass, CYP3A5 genotype, sex, age and time after transplant influence the tacrolimus individual dose requirement. Because hematocrit is highly variable in kidney transplant patients and increases substantially after kidney transplantation, hematocrit is a key factor in the interpretation of tacrolimus whole blood concentrations.

Following organ engraftment, initial dosing of tacrolimus is based on recipient weight and adjusted by measured C(0) concentrations. The bioavailability and elimination of tacrolimus are affected by the patients CYP3A5 genotype. Prospective data of the clinical advantage of knowing patient's CYP3A5 genotype prior to transplantation are lacking. A nonparametric population model was developed for tacrolimus in renal transplant recipients. Data from 99 patients were used for model development and validation. A three-compartment model with first-order absorption and lag time from the dosing compartment described the data well. Clearances and volumes of distribution were allometrically scaled to body size. The final model included fat-free mass, body mass index, hematocrit, time after transplantation, and CYP3A5 genotype as covariates. The bias and imprecision were 0.35 and 1.38, respectively, in the external data set. Patients with functional CYP3A5 had 26% higher clearance and 37% lower bioavailability. Knowledge of CYP3A5 genotype provided an initial advantage, but only until 3-4 tacrolimus concentrations were known. After this, a model without CYP3A5 genotype predicted just as well. The present models seem applicable for clinical individual dose predictions but need a prospective evaluation., (© 2013 The Authors Transplant International published by John Wiley & Sons Ltd on behalf of Steunstichting ESOT.)

Background: New-onset diabetes after transplantation may be associated with the use of tacrolimus (Tac) causing impaired insulin release or reduced insulin sensitivity. Such effects have not been studied in renal transplant recipients receiving traditional twice-daily tacrolimus (TacBID) and then compared to the new once-daily prolonged release formulation of tacrolimus (TacOD)., Methods: We performed a prospective crossover study of 20 stable non-diabetic renal transplant recipients. All patients underwent one hyperglycaemic clamp on TacBID (3.8 ± 2.2 mg/day) and a new clamp 4-6 weeks after a 1:1 mg/day switch to TacOD (4.0 ± 2.8 mg/day)., Results: Tac trough concentrations decreased from 6.6 ± 2.9 to 5.4 ± 1.4 μg/mL (P = 0.037) and Tac max from 21.3 ± 8.4 to 15.2 ± 3.5 μg/L (P = 0.001). Tac AUC(0-24) was reduced from 265 ± 112 to 218 ± 47 μg × h/L (P = 0.12). The hyperglycaemic clamp did not detect any change in insulin sensitivity index after conversion [0.26 ± 0.21 versus 0.26 ± 0.25 μmol/min/kg/(pmol/L insulin), P = 0.99] nor any change in first (334 ± 274 versus 353 ± 248 μIU × min/mL, P = 0.41) or second phase insulin secretion (224 ± 155 versus 263 ± 210 μIU × min/mL/mmol glucose, P = 0.60) on TacBID versus TacOD., Conclusions: Conversion from standard TacBID to TacOD on a 1:1 mg basis is safe. In spite of a reduced Tac exposure, there was no change in insulin release or sensitivity in renal transplant recipients.

Background: Mycophenolic acid (MPA) is widely used as part of immunosuppressive regimens following allograft transplantation. The large pharmacokinetic (PK) and pharmacodynamic (PD) variability and narrow therapeutic range of MPA provide a potential for therapeutic drug monitoring. The objective of this pilot study was to investigate the MPA PK and PD relation in combination with belatacept (2nd generation CTLA4-Ig) or cyclosporine (CsA)., Methods: Seven renal allograft recipients were randomized to either belatacept (n = 4) or cyclosporine (n = 3) based immunosuppression. Samples for MPA PK and PD evaluations were collected predose and at 1, 2 and 13 weeks posttransplant. Plasma concentrations of MPA were determined by HPLC-UV. Activity of inosine monophosphate dehydrogenase (IMPDH) and the expressions of two IMPDH isoforms were measured in CD4+ cells by HPLC-UV and real-time reverse-transcription PCR, respectively. Subsets of T cells were characterized by flow cytometry., Results: The MPA exposure tended to be higher among belatacept patients than in CsA patients at week 1 (P = 0.057). Further, MPA concentrations (AUC0-9 h and C0) increased with time in both groups and were higher at week 13 than at week 2 (P = 0.031, n = 6). In contrast to the postdose reductions of IMPDH activity observed early posttransplant, IMPDH activity within both treatment groups was elevated throughout the dosing interval at week 13. Transient postdose increments were also observed for IMPDH1 expression, starting at week 1. Higher MPA exposure was associated with larger elevations of IMPDH1 (r = 0.81, P = 0.023, n = 7 for MPA and IMPDH1 AUC0-9 h at week 1). The maximum IMPDH1 expression was 52 (13-177)% higher at week 13 compared to week 1 (P = 0.031, n = 6). One patient showed lower MPA exposure with time and did neither display elevations of IMPDH activity nor IMPDH1 expression. No difference was observed in T cell subsets between treatment groups., Conclusion: The significant influence of MPA on IMPDH1 expression, possibly mediated through reduced guanine nucleotide levels, could explain the elevations of IMPDH activity within dosing intervals at week 13. The present regulation of IMPDH in CD4+ cells should be considered when interpreting measurements of IMPDH inhibition.

Background: Obesity is a common problem following renal transplantation. Rimonabant, a cannabinoid-1 receptor blocker, offers a new approach for reducing obesity., Methods: The potential pharmacokinetic interaction between rimonabant and cyclosporine A (CsA, n=10) and tacrolimus (Tac, n=8) was assessed in stable renal transplant recipients 6.2 (0.9-21.7) years posttransplant. A 12-hour pharmacokinetic profile was obtained before and after two months of concomitant treatment with 20 mg rimonabant each morning., Results: Rimonabant treatment induced a moderate, but significant increase in CsA AUC0-12 (19.8+/-16.1 %, P=0.005). Cmax and C2 values tended to increase whereas C0 remained unaffected. Tac pharmacokinetics was not significantly affected by rimonabant treatment. Eleven of 18 patients experienced adverse events. Two patients reported depressions and one reported severe nightmares., Conclusions: The effect on CsA pharmacokinetics is probably of marginal clinical relevance since trough concentrations were unaltered, but CsA concentrations should probably be more closely monitored if rimonabant treatment is initiated, preferably by C2 monitoring.

Background: Physiologic functions that may affect pharmacokinetics of drugs are altered in elderly patients. The current study was performed to elucidate the effect of age on cyclosporine A (CsA) pharmacokinetics in renal transplant recipients., Method: Twenty-five renal transplant recipients on CsA treatment were included in the study. CsA doses were adjusted by C2 monitoring. The patients were divided into two groups based on age; elderly: more than 65 years (n=11, mean 73 years) and younger: 18 to 64 years (n=14, mean 43 years). A full 12-hr pharmacokinetic profile was performed during stable phase. CsA whole blood and intracellular T-lymphocytes concentrations (first 6 hr) were measured. Genotyping of the CYP3A5*1/*3 and ABCB1 (C1236T, G2677T, C3435T) polymorphisms and quantification of whole blood mRNA ABCB1 expression were performed in all patients., Results: Elderly patients achieved target C2 levels with lower CsA doses than the younger patients (4.3+/-0.8 vs. 6.1+/-2.1 mg/day/kg, P=0.025) because of lower clearance of CsA (22.7+/-5.1 vs. 30.5+/-11.1 L/hr, P=0.031). Elderly patients also showed 44% higher intracellular-to-whole blood CsA ratio than younger patients (P=0.02). Neither the CYP3A5*1, the ABCB1 genotypes nor mRNA ABCB1 expression revealed any significant influence on CsA pharmacokinetics., Conclusion: The clearance of CsA decreased with increasing age. In addition, elderly patients had a significant larger proportion of the whole blood CsA concentration located at the site of action (within T lymphocytes). This indicates that in elderly recipients it might be safe to aim for an even lower whole blood target levels than current guidelines propose.

Background: The calcimimetic drug cinacalcet offers a novel therapeutic option to treat post-transplant hypercalcemia and hyperparathyroidism; however, the interaction with calcineurin inhibitors and mycophenolate has not been evaluated., Methods: In the present study the effects of cinacalcet on the pharmacokinetics of cyclosporine A (CsA), tacrolimus (Tac) and mycophenolate were investigated in 14 renal transplant recipients with stable renal function (mean creatinine 126.4 +/- 45.3 micromol/L). The patients were treated with either CsA (n = 8) or Tac (n = 6) in combination with mycophenolate/azathioprine and steroids. Twelve-hour pharmacokinetic investigations to measure CsA and its six main metabolites, Tac and mycophenolate concentrations were performed before and after 1-week treatment with 30 mg cinacalcet once daily., Results: Cinacalcet treatment induced a significant 14.3 +/- 12.1% decrease in Tac AUC(0-12) (P = 0.039). Tac C(max), T(max) and T(1/2) also tended to decrease. The pharmacokinetics of CsA and mycophenolate were not significantly affected by concomitant treatment with cinacalcet. However, the secondary CsA metabolite, AM19, showed a significant increase of 9.0 +/- 9.5% during cinacalcet treatment (P = 0.040). Renal function decreased significantly from 78 +/- 11 to 72 +/- 12 mL/min (P = 0.019) and correlated with the increased levels of metabolite AM19 in the CsA group. Renal function was unchanged in the Tac group., Conclusion: Cinacalcet treatment showed a moderate effect on the Tac, but not CsA or mycophenolate, pharmacokinetics after 1-week concomitant treatment. This interaction appears to have minor clinical relevance. However, it is advisable to monitor renal function in CsA-treated patients due to the observed decrease in renal function.

Background: Mycophenolic acid (MPA) mediates immunosuppressive effects by inhibiting inosine monophosphate dehydrogenase (IMPDH). Induction of IMPDH activity has been observed in whole blood and erythrocyte samples during immunosuppressive therapy. Information concerning the mechanisms for increased IMPDH activity is limited and the potential implications of induction have been debated., Methods: Whole blood, CD4+ cell, and reticulocyte samples were collected from 30 renal transplant patients pre- and posttransplantation. The expressions of two IMPDH isoforms, type 1 and 2, were analyzed by real-time reverse-transcription polymerase chain reaction and quantified using a housekeeping gene index. The IMPDH activity was determined by ultraviolet high-performance liquid chromatography., Results: Transplantation and the initiation of immunosuppressive therapy was associated with increased IMPDH1 (50-88%, P<0.0005) and decreased IMPDH2 (42-56%, P<0.0005) expression. In CD4+ cells, however, IMPDH2 increased (15%, P=0.009). These changes are probably related to glucocorticoid effects. Two weeks posttransplant, MPA-treated patients displayed elevated IMPDH 1 and 2 in reticulocytes, suggesting enzyme induction in these cells during prolonged MPA therapy. Patients with acute rejection during follow-up demonstrated higher IMPDH2 expression in CD4+ cells pretransplant than nonrejecting patients (median expression 1.26 vs. 0.87 respectively, P=0.017)., Conclusions: Knowledge of changes in IMPDH 1 and 2 expression after transplantation and initiation of immunosuppression is important considering the action of MPA on IMPDH and the potential for pharmacodynamic monitoring of MPA by measuring IMPDH activity. The expression of IMPDH2 in CD4+ cells pretransplant may be an indicator of immune activation.

Thrombotic microangiopathy (TMA) and hemolytic uremic syndrome (HUS) represent serious threats to kidney allograft recipients. During a 4-year period, among 850 kidney transplantations, seven recipients with primary HUS and seven recipients (eight transplants) with previous or de novo TMA/HUS were identified and given calcineurin inhibitor (CNI)-free immunosuppression by sirolimus (SRL), mycophenolate mofetil and steroids. Thirteen out of 15 transplantations were successful in the long term; resulting in a mean creatinine of 101 mumol/L (16.4 months follow-up). In patients maintained on CNI-free regimen, no TMA/HUS recurrences were observed. A high rate of acute rejections (53%) may indicate insufficient immunosuppressive power and/or a causative relationship between TMA/HUS and rejection. Wound-related complications were abundant (60%), and call for surgical/immunosuppressive countermeasures. Our experience supports the idea that CNI's are major offenders in TMA/HUS induction. Total CNI elimination seems essential, as the nephrotoxic combination CNI + SRL may promote TMA. Features of TMA/HUS should be carefully explored in recurrent 'high responders'.

Objective: Mycophenolic acid (MPA) exerts its immunosuppression by inhibiting inosine 5'-monophosphate dehydrogenase (IMPDH), depleting activated lymphocytes of guanine nucleotides and retarding their proliferation. An optimal strategy for monitoring has not been established for mycophenolate mofetil (MMF) in renal transplantation, and clinical investigations of the pharmacokinetic-pharmacodynamic relationship are warranted., Material and Methods: Mycophenolic acid pharmacokinetics and whole blood cell IMPDH activity were investigated in two separate groups of renal allograft recipients. One group was studied within the 12-h dose interval, while the second group was examined by pre-dose samples pre-transplant and then repeatedly during 8 weeks post-transplant., Results: An inverse relationship between plasma MPA and IMPDH activity within the dose interval was demonstrated. Minimum IMPDH activity was a median 8 % of values pre-MMF dose, coinciding with the MPA peak. Six hours post-dose, IMPDH activity had returned to pre-dose values. Patients receiving MMF had a 4.5-fold higher pre-dose enzyme activity than transplanted patients without MMF. During the 8 weeks post-transplant, the median MPA trough concentration was fairly stable. Following an initial decrease during the first 4 days post-transplant, IMPDH activity gradually increased during the 40 days post-transplant, reaching 5-fold the pre-transplant values., Conclusions: Provided that the changes in IMPDH activity in whole blood cells predict the clinical effect, these pharmacokinetic-pharmacodynamic findings may prove useful in the attempts to identify optimal timing and range for the monitoring of mycophenolate in renal transplantation. The question of whether MPA concentrations or measurements of IMPDH activity per se will be the optimal way of monitoring this immunosuppressant remains open and will only be answered by prospective clinical testing.

Therapeutic drug monitoring of mycophenolic acid (MPA) in combination with cyclosporine 2-h concentration (CsA C2, n = 68) or tacrolimus trough concentration (n = 10) was investigated by repeated measurements of MPA and MPA-glucuronide (MPAG) trough concentrations in renal allograft recipients during the first 3 months post-transplant. The acute rejection rate was lower (19% vs. 43%; P < 0.05) in patients achieving CsA C2 target range during the first week (1600-2000 microg/l), n = 26, compared with those who did not, n = 42. Median MPA concentration was 0.9 and 1.2 microg/ml in patients within or below C2 range, respectively (P = 0.19). CsA C2 correlated with MPAG-to-MPA ratio (P < 0.01, r = 0.91) and gamma-glutamyl-transpeptidase (GGT, P < 0.01, r = 0.86). Total MPA concentration increased during the 3 months, but not in patients on tacrolimus. High CsA C2 lowered the acute rejection rate and plasma MPA. High CsA C2 is associated with elevated GGT, probably because of cholestatic effects, which explain the increased MPAG-to-MPA ratio. Increasing MPA concentration is ascribed to per-protocol CsA C2 reductions. In conclusion, CsA may confound the relationship between MPA and the incidence of rejection, and contribute to the difficulty of obtaining a therapeutic range for MPA in clinical practice.

Presently, there is little knowledge regarding cyclosporine (CsA) concentration at 2 hr post-dose (C2) monitoring in maintenance patients. This study evaluates the actual C2 range in stable renal transplant recipients (who underwent transplantation >12 months ago). In addition, we investigated whether underexposure or overexposure to CsA (assessed by C2) affects graft function (as measured by serum [S]-creatinine). All renal transplant recipients in Norway receiving CsA were asked to participate; 1447 fulfilled the criteria. Valid C2 and CsA trough concentration (C0) measurements were performed in 1032 renal transplant recipients (71%) monitored by C0. Target C0 level was 75 to 125 mumol/L. CsA levels were measured using a Cloned Enzyme Donor Immunoassay method, and all analyses were performed in the same laboratory (overall mean [+/-standard deviation] CsA C0=112+/-31 mug/L, CsA C2=697+/-211 mug/L [range 81-1580 mug/L], CsA dose [mg/day]=208+/-61, CsA dose [mg/kg/day]=2.8+/-1.1, and S-creatinine=141+/-58 mumol/L). A univariate analysis of variance showed that patients with C2 levels between 700 and 800 mug/L (n=203, S-creatinine=136+/-49 mumol/L) had significantly lower S-creatinine levels compared with patients with C2 levels greater than 950 mug/L (n=94, S-creatinine=152+/-56 mumol/L) (P<0.02). The same was true for patients with C2 levels less than 450 mug/L (n=95, S-creatinine 141+/-72 mumol/L) (P<0.05) when compared with patients with C2 levels greater than 950 mug/L. There was no significant difference in S-creatinine between patients in the low and intermediate C2 group; 666 patients had C0 levels in the therapeutic range (75-125 mumol/L). A linear regression showed a significant relation between S-creatinine and C2 for these patients (P=0.03). The corresponding relation between S-creatinine and C0 was nonsignificant (P=0.3). Monitoring of C2 in maintenance patients is a valuable tool to detect overexposure to CsA. Until results from prospective studies are available, we recommend C0 in the therapeutic range and reduction in CsA in overexposed patients, aiming at a C2 value between 700 and 800 mug/L.

Mycophenolic acid, the active moiety of mycophenolate mofetil, inhibits the enzyme inosine monophosphate dehydrogenase. The main metabolite, mycophenolic acid glucuronide, has no immunosuppressive effect. Reported protein bindings are 97% for mycophenolic acid and 82% for mycophenolic acid glucuronide. Considerable intraindividual and interindividual variability in mycophenolic acid pharmacokinetics has been observed. Data on the variability of mycophenolic acid free fraction in plasma are sparse but may be relevant when discussing whether therapeutic drug monitoring of this drug is warranted. The authors describe a fully automated method for the determination of free concentrations by dialysis across a membrane followed by concentration of the dialysate on a trace enrichment column and liquid chromatography. Total concentrations are measured by protein precipitation and direct injection on the trace enrichment column. Plasma concentrations as low as 6 ng/mL free mycophenolic acid and 1 microg/mL free mycophenolic acid glucuronide can be measured with between-day coefficient of variation less than 15% and 6%, respectively. Stability testing confirmed that plasma samples could be stored for 14 days at 4 degrees C or -20 degrees C and at room temperature for approximately 12 hours without significant changes in free concentrations. Predose total and free concentrations of mycophenolic acid and mycophenolic acid glucuronide were determined in 27 samples from stable renal allograft recipients treated with mycophenolate mofetil, cyclosporin, and steroids. Total concentrations ranged from 0.57 to 16.2 microg/mL mycophenolic acid and 36 to 199 microg/mL mycophenolic acid glucuronide. Free concentrations ranged from 13 to 210 ng/mL mycophenolic acid and 8 to 58 microg/mL mycophenolic acid glucuronide. The method presented here has been successfully applied to measure free mycophenolic acid and free mycophenolic acid glucuronide in clinical samples. Further investigations may provide important data to support the identification of principles and target ranges for the monitoring of mycophenolic acid in the immunosuppressive therapy of organ transplant recipients.

Atorvastatin is increasingly used as a cholesterol-lowering agent in solid organ transplant recipients receiving cyclosporine A (CsA). However, the potential bilateral pharmacokinetic interaction between atorvastatin and CsA in renal transplant recipients has not previously been examined. Baseline 12-h CsA pharmacokinetic investigation was performed in 21 renal transplant recipients and repeated after 4 weeks of atorvastatin treatment (10 mg/ d). At week 4, 24-h pharmacokinetics of atorvastatin was also performed. All patients received basiliximab induction followed by CsA and prednisolone immunosuppression. Compared with historic controls, CsA-treated patients showed, on average, sixfold higher plasma HMG-CoA reductase inhibitory activity after 4 weeks of atorvastatin treatment (p < 0.05). Atorvastatin had a moderate effect on the pharmacokinetics of CsA and reduced the AUC0-12 (area under curve, 0-12h) by 9.5 +/- 18% (p = 0.013) and Cmax (maximal concentration) by 13.5 +/- 24% (p =0.009), while C12 (trough level) was unchanged (p =0.42). Total and LDL cholesterol decreased by 26.8 +/- 8.4% (p < 0.0001) and 41.5 +/- 11.0% (p < 0.0001), respectively. Bilateral pharmacokinetic interaction between atorvastatin and CsA resulted in sixfold higher plasma HMG-CoA reductase inhibitory activity, but only a moderate decrease in systemic exposure of CsA.

Background: Glipizide is an oral antidiabetic drug that has been used in the treatment of post-transplant diabetes mellitus (PTDM). However, a published case report has indicated a possible interaction of glipizide with cyclosporine (CsA) pharmacokinetics in two renal transplant (tx) patients. The aim of this open prospective study was to investigate whether glipizide interacts with CsA pharmacokinetics in renal tx patients with PTDM., Methods: Eleven renal tx patients (29-74 years of age) with PTDM who received Sandimmun Neoral as part of their immunosuppressive therapy were investigated. No patients had suffered any significant rise in serum creatinine (20%) from any cause over the last 2 wk before the study. Mean S-creatinine was 137 mumol/L (87-220). The mean CsA dose and whole blood concentration remained unchanged during the study. CsA whole blood concentrations were monitored over 12 h in all patients in random order, both on and off glipizide treatment. Blood samples were drawn immediately before the morning dose of CsA was given (trough) and 0.5, 1, 1.5, 2, 3, 4, 6 and 12 h after administration., Results: Whole blood trough CsA concentration was not altered by glipizide treatment, 256 +/- 76 micrograms/L off and 242 +/- 73 micrograms/L (mean +/- SD) with glipizide coadministration. The area under the curve (AUC) and terminal half-life of CsA remained unchanged with glipizide treatment: 6391 +/- 1483 micrograms/L per h and 7.3 +/- 1.5 h without; and 6279 +/- 1601 micrograms/L per h and 7.1 +/- 1.8 h with glipizide, respectively. No change in the CsA peak concentration (Cmax) was observed: 1507 +/- 406 micrograms/L without and 1469 +/- 538 micrograms/L with glipizide coadministration., Conclusion: CsA pharmacokinetics is not significantly altered by glipizide coadministration.

Background: Azathioprine (AZA) is widely used in organ transplantation. Common practice is to adjust dose according to body weight only, despite documented pharmacokinetic variability. The purpose of this study was to investigate whether high-dose AZA treatment monitored by 6-thioguanine nucleotides (6-TGN) levels reduces the incidence of rejection episodes in renal transplantation without a corresponding increase in myelotoxicity., Methods: Patients receiving cyclosporine, steroids, and AZA were randomized into either the low-dose AZA group (3 mg/kg on day 0, then 2 mg/kg/day the first week and 1 mg/kg/day thereafter) or the high-dose AZA group. In the latter, AZA was started at 5 mg/kg/day and then adjusted to keep 6-TGN concentrations (measured twice weekly) between 100 and 200 pmol/8 x 10(8) RBCs., Results: A total of 360 transplant recipients were included in the final analysis. The cumulative incidence of first rejection episodes was reduced by 21%, from 62.8% in the low-dose group to 49.4% in the high-dose group (difference: 13.3%; 95% confidence interval: 3.2-23.5). Similar results were found in subgroups according to HLA-DR match. The 6-TGN concentration was significantly higher in the high-dose AZA group during the first month, and the reduction in rejection episodes was achieved in the same period. A larger proportion of patients in the high-dose group had nadir white blood cell count below 2.0 x 10(9) leukocytes/L (13.3% vs. 4.4%; difference: 8.9%; confidence interval: 3.1-14.7)., Conclusions: High-dose AZA therapy in a triple-drug regimen, monitored by 6-TGN, will keep myelotoxicity within acceptable limits with the benefit of a reduction in acute rejection episodes.

Monitoring of azathioprine (AZA) therapy by the measurement of 6-thioguanine nucleotides (6-TGN) concentrations in red blood cells (RBC) may improve safety and ensure optimal immunosuppressive effects of AZA in organ transplantation. The authors explored the rationale for such monitoring by measuring thiopurine metabolites in peripheral blood cell types that are more relevant to the effects and kinetics of AZA and its active metabolites. Neutrophil granulocytes were isolated by density gradient centrifugation, and CD4+ lymphocytes and reticulocytes by using specific immunomagnetic beads. In neutrophils, 6-TGN concentrations had median measurements 31 times higher than in RBCs. In contrast to the high methylated mercaptopurine (me-MP) concentrations in RBCs, these metabolites were not detected in the neutrophils. Thiopurine metabolite levels were lower than the analytic limit of detection in all the CD4+ samples. The concentrations of 6-TGN and me-MPs were lower in reticulocytes than in RBCs in general, indicating that thiopurine metabolites are taken up by RBCs in the circulation. This study's findings, that 6-TGN concentrations are very high in neutrophils, whereas me-MPs are undetectable, many explain the specific neutropenic adverse effect of AZA. The results also add support to monitoring AZA through measurements of 6-TGN and me-MPs in RBCs.

The objectives of this study were to establish monitoring of azathioprine (AZA) treatment in renal allograft recipients by red blood cell (RBC) 6-thioguanine nucleotide (6-TGN) measurements and to characterize the variability of RBC thiopurine methyltransferase (TPMT) activity and the effects on 6-TGN levels and the incidence of rejection episodes. In 82 renal allograft recipients, the effect of standard AZA dosage (3 mg/kg tapered to 1 mg/kg) was compared with higher dosages (3 mg/kg for several days) under 6-TGN monitoring. The authors measured TPMT in these patients and in a group not receiving AZA. The authors did not find an inverse correlation between RBC TPMT activity and 6-TGN concentrations, and baseline TPMT activity did not predict the incidence of rejection episodes The slight increase in RBC TPMT activity after transplant was associated with the use of furosemide rather than AZA; in the five patients receiving furosemide for less than 10 days, TPMT activity declined. The higher AZA dosage in the 6-TGN monitored group was not sufficient to increase RBC 6-TGN to target levels (100 to 200 pmol/8 x 10(8) RBC); median 6-TGN levels were similar in the two groups, as was the incidence of rejection episodes. Based on these findings, the authors suggest that higher dosages be studied in conjunction with 6-TGN monitoring, to explore the possibilities for therapeutic improvements.

Thioguanine nucleotides (6-TGN) are intracellular metabolites that may contribute to the antiproliferative effects of AZA. The objectives of our study were to describe the variability of 6-TGN concentrations during AZA therapy and to investigate possible correlations between 6-TGN levels and subsequent myelosuppression. We measured 6-TGN concentrations in RBC of 65 renal transplant recipients from day 0 until 11-64 days after transplantation. High 6-TGN concentrations were observed in relation to elevated S-creatinine. In 15 patients, 6-TGN concentrations above 200 pmol/8 x 10(8) RBCs were measured (high 6-TGN group: mean maximal 6-TGN = 552 pmol/8 x 10(8) RBCs, SE = 91). In the remaining 50 patients, mean maximal 6-TGN was 82 pmol/8 x 10(8) RBCs, SE = 6.1 (low t-TGN group). In the former group, mean S-creatinine measured on the day of maximal 6-TGN was 466 mumol/L (SE = 62.3), while in the latter it was 190 (SE = 14.7). In the high 6-TGN group, we observed a lower mean nadir neutrophil count than in the low 6-TGN group (3.4 vs. 5.1 x 10(9) neutrophils/L). The nadir neutrophil count occurred, on the average, 12.7 days after maximal 6-TGN in the high 6-TGN group, with no such delay in the low 6-TGN group. This study demonstrates for the first time that 6-TGN in RBCs may rise to very high levels during impaired renal function. Furthermore, the results support the hypothesis that myelosuppressive side effects of AZA therapy correlate with 6-TGN concentrations. Renal transplant recipients may benefit from the monitoring of AZA through RBC 6-TGN measurements.

The purpose of this study was to examine the pharmacokinetics of mercaptopurine (6-MP) and thioguanine nucleotides (6-TGN) during azathioprine treatment. Plasma profiles and urinary excretion of 6-MP and 6-TGN concentrations in red blood cells (RBCs) were measured repeatedly during the first 3 weeks following transplantation in 10 adults, who had received kidney grafts from living related donors. Mean maximal 6-MP plasma concentration (Cmax) was 340 nmol/L (SD = 290), mean time to Cmax (Tmax) was 2 h (SD = 1.8), and mean area under the plasma concentration-time curve (AUC) was 930 nmol/L/h (SD = 770). The mean fraction of azathioprine dose excreted as 6-MP in urine was 1.32% (SD = 1.11). Up to eightfold variability of Cmax and AUC was observed from day to day within each patient. The correlation between 6-MP AUC and amount excreted in the urine was weak (r = 0.37, 95% CI from 0.02 to 0.64). In this group of patients the observed 6-TGN levels in RBCs were low; maxima during the observation period ranged from undetectable to 250 pmol/8 x 10(8) RBCs. In individual patients, 6-TGN levels were relatively stable throughout the dosing interval ("within-dose-interval-CV" < 19%), even when sharp and high 6-MP peaks in plasma were observed.

Hypertension has emerged as a frequent side effect in transplant recipients on effective doses of cyclosporine (CsA). To control hypertension in renal transplant patients, calcium channel blockers have been used; some of these, however, have been shown to cause significant increases in CsA levels. These findings point out that possible interactions of each calcium antagonist with CsA deserve investigation. We performed an open, placebo-controlled study in 12 stable renal transplant recipients to determine whether short-term isradipine influences CsA pharmacokinetics. All patients had mild to moderate hypertension and received triple immunosuppressive therapy with CsA, azathioprine, and prednisolone. Throughout a 4-week period of isradipine treatment, blood CsA levels (specific and nonspecific monoclonal antibodies) remained stable. The mean trough specific level was 121 +/- 14 micrograms/L following placebo, compared to 120 +/- 14 micrograms/L during isradipine. Corresponding non-specific values were 465 +/- 68 and 474 +/- 63 micrograms/L. Also, values for Cmax, AUC, and t1/2 were not significantly changed following 4 weeks of isradipine. Mean arterial pressure was significantly reduced at the end of the study. This study implies that isradipine does not influence CsA metabolism. Further studies should be carried out to determine its long-term effects on CsA pharmacokinetics and renal function in transplanted patients.