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TV-46000 is a long-acting subcutaneous antipsychotic that uses a novel copolymer drug delivery technology in combination with a well-characterized molecule, risperidone, that is in clinical development as a treatment for schizophrenia. A population pharmacokinetic (PPK) modeling and simulation approach was implemented to identify TV-46000 doses and dosing schedules for clinical development that would provide the best balance between clinical efficacy and safety. The PPK model was created by applying pharmacokinetic data from a phase 1 study of 97 patients with a diagnosis of schizophrenia or schizoaffective disorder who received either single or repeated doses of TV-46000. The PPK model was used to characterize the complex release profile of the total active moiety (TAM; the sum of the risperidone and 9-OH risperidone concentrations) concentration following subcutaneous injections of TV-46000. The PK profile was best described by a double Weibull function of the in vivo release rate and by a 2-compartment disposition and elimination model. Simulations were performed to determine TV-46000 doses and dosing schedules that maintained a median profile of TAM concentrations similar to published TAM exposure following oral risperidone doses that have been correlated to a 40% to 80% dopamine-D2 receptor occupancy therapeutic window. The simulations showed that therapeutic dose ranges for TV-46000 are 50 to 125 mg for once-monthly and 100 to 250 mg for the once every 2 months regimens. This PPK model provided a basis for prediction of patient-specific exposure and dopamine-D2 receptor occupancy estimates to support further clinical development and dose selection for the phase 3 studies.

Objective Exposure-response (E-R) models were developed to provide a description of the time-course of treatment effect for monthly and quarterly dosing regimens of fremanezumab. Background Fremanezumab is a monoclonal antibody for preventive treatment of episodic migraine (EM) and chronic migraine (CM). In phase 2b and 3 clinical studies of fremanezumab, significant reductions in migraine and headache days and other clinical endpoints were observed for patients with EM and patients with CM. Development of E-R models relating individual-specific measures of drug exposure to clinical endpoints provides a more granular understanding of the expected effects of different doses on therapeutic outcomes by accounting for variability in pharmacokinetic (PK) properties. Methods Data from 2 phase 2b and 2 phase 3 studies of adults with EM or CM were used. Individual exposures were calculated from a population PK model and related to monthly migraine days in EM and moderate-severe (M/S) headache days in CM. Model-based stochastic simulations were performed to compare predicted responses for the various treatment regimens. Results The effect of average fremanezumab concentration compared to placebo on the reduction in migraine days and M/S headache days was predicted by the models to be similar for 225 mg monthly and 675 mg once quarterly over time for both EM and CM patients. Both regimens were associated with better response than placebo. A similar percent of EM and CM responders was predicted across the range of observed body weights. Conclusions Exposure-response evaluations showed that both monthly (225 mg) and quarterly (675 mg) fremanezumab dosing regimens were appropriate in achieving clinical benefit in adult patients with EM or CM.

Background Potential fremanezumab doses for pediatric patients were evaluated using pharmacokinetic modeling and simulation. An open-label phase 1 pharmacokinetic and safety study was conducted in pediatric patients with migraine. This study’s results together with refinement of the adult population pharmacokinetic model were used to determine fremanezumab dose recommendations for phase 3 pediatric studies. Methods Initial application of the adult model suggested that a 75 mg dose in pediatric patients would match exposures determined safe and efficacious in adults; thus, in the phase 1 study, 15 patients, aged 6–11 years and weighing 17–45 kg received a single subcutaneous 75 mg fremanezumab dose. The sparse pharmacokinetic data collected were used to refine the adult model and simulate concentration-time profiles for monthly subcutaneous doses (60 to 225 mg) in a virtual pediatric population. Results In the phase 1 pediatric study, the safety profile was similar to that of adults. A two-compartment model with first-order absorption and elimination and body weight effects on clearance and central volume was found to adequately describe the pediatric pharmacokinetic data. Conclusions Using exposure matching to the effective adult fremanezumab dose (225 mg subcutaneous monthly), modeling and simulations predict recommended dose of 120 mg in pediatric patients weighing

AIMS SD-1077, a selectively deuterated precursor of dopamine (DA) structurally related to L-3,4-dihydroxyphenylalanine (L-DOPA), is under development for treatment of motor symptoms of Parkinson's disease. Preclinical models have shown slower metabolism of central deuterated DA. The present study investigated the peripheral pharmacokinetics (PK), metabolism and safety of SD-1077. METHODS Plasma and urine PK of drug and metabolites and safety after a single oral 150 mg SD-1077 dose were compared to 150 mg L-DOPA, each in combination with 37.5 mg carbidopa (CD) in a double-blind, two-period, crossover study in healthy volunteers (n = 16). RESULTS Geometric least squares mean ratios (GMRs) and 90% confidence intervals (90% CI) of SD-1077 vs. L-DOPA for Cmax , AUC0-t , and AUC0-inf were 88.4 (75.9-103.1), 89.5 (84.1-95.3), and 89.6 (84.2-95.4), respectively. Systemic exposure to DA was significantly higher after SD-1077/CD compared to that after L-DOPA/CD, with GMRs (90% CI) of 1.8 (1.45-2.24; P = 0.0005) and 2.06 (1.68-2.52; P

Reslizumab 3.0 mg/kg has demonstrated efficacy in clinical studies of patients with eosinophilic asthma and a history of exacerbations. A population pharmacokinetic (PK) model was developed to determine whether 3.0 mg/kg weight-based dosing is appropriate to obtain consistent reslizumab exposures in all patients. PK data in healthy volunteers and patients ≥12 years with moderate to severe asthma, eosinophilic asthma, or nasal polyposis were analyzed from 4 phase 1, 2 phase 2, and 2 phase 3 studies of intravenous (IV) reslizumab (N = 804). Covariates evaluated included age, race, sex, baseline weight, renal and liver function, concomitant medications, and antidrug antibody status. Exposure-response models were developed to characterize key efficacy (blood eosinophil levels, forced expiratory volume in 1 second [FEV1 ], Asthma Control Questionnaire [ACQ-7] scores), and safety end points (muscle disorder adverse events [AEs]). Vial-based dosing was evaluated as an alternative to weight-based dosing. IV reslizumab PK was accurately described by a 2-compartment PK model with 0-order input and first-order elimination. Body weight was the only covariate that significantly influenced PK parameters. However, with weight-based dosing, comparable steady-state exposures were observed across high and low body weights. Greater eosinophil lowering and longer response duration were observed with increasing dose; exposure-related effects on FEV1 and ACQ-7 were also seen, demonstrating the clinical importance of a dosing regimen to optimize reslizumab exposure. The probability of a muscle disorder AE appeared to increase with increasing exposure. Steady-state exposure measures were similar for both dosing regimens, showing vial-based dosing as an alternative method of achieving the benefits of weight-based dosing.

Aims Fremanezumab is a fully humanized IgG2 Δa/κ monoclonal antibody specific for calcitonin gene-related peptide developed and approved for the preventive treatment of migraine in adults. The population pharmacokinetics (PK) of fremanezumab were characterized in healthy subjects and patients with chronic migraine and episodic migraine, including the effects of intrinsic and extrinsic factors on PK variability. Methods Nonlinear mixed effects modelling was performed using NONMEM with data from 7 phase 1-3 clinical trials evaluating selected intravenous and subcutaneous dose regimens. The influence of covariates on fremanezumab PK was assessed and model evaluation was performed through visual predictive checks. Results A 2-compartment model with first-order absorption and elimination described the PK data well. Typical values for fremanezumab central clearance (0.0902 L/d) and central distribution volume (1.88 L) for a 71-kg subject were consistent with previously reported values for IgG antibodies. Higher body weight was associated with increased central clearance and distribution volume. Effects of other covariates (age, albumin, renal function, sex, race, injection site, and acute, analgesic and preventive medication use for migraine) were not found to statistically significantly influence fremanezumab PK. There was no indication of reduced exposure in participants with positive anti-drug antibody status or with mild to moderate hepatic impairment. Absolute bioavailability was estimated at 0.658. Conclusions A comprehensive population PK model was developed for fremanezumab following intravenous and subcutaneous administration in healthy subjects and patients with chronic migraine or episodic migraine, which will be used to further evaluate exposure-response relationships for efficacy and safety endpoints.

Aim The objective of this population pharmacokinetic (PK) analysis was to provide guidance for the dosing interval of daptomycin in patients undergoing continuous renal replacement therapy (CRRT). Methods A previously published population PK model for daptomycin was updated with data from patients undergoing continuous veno-venous haemodialysis (CVVHD; n = 9) and continuous veno-venous haemodiafiltration (CVVHDF; n = 8). Model-based simulations were performed to compare the 24 h AUC, Cmax and Cmin of daptomycin following various dosing regimens (4, 6, 8, 10, and 12 mg kg−1 every [Q] 24 h and Q48 h), with the safety and efficacy exposure references for Staphylococcus aureus bacteraemia/right-sided infective endocarditis. Results The previously developed daptomycin structural population PK model could reasonably describe data from the patients on CRRT. The clearance in patients undergoing CVVHDF and CVVHD was estimated at 0.53 and 0.94 l h−1, respectively, as compared with 0.75 l h−1 in patients with creatinine clearance (CrCl) ≥ 30 ml min−1. Daptomycin Q24 h dosing in patients undergoing CRRT resulted in optimal exposure for efficacy, with AUC comparable to that in patients with CrCl ≥ 30 ml min−1. In contrast, Q48 h dosing was associated with considerably lower AUC24–48h in all patients for doses up to 12 mg kg−1 and is therefore inappropriate. Conclusions Q24 h dosing of daptomycin up to 12 mg kg−1 provides comparable drug exposure in patients on CVVHD and in those with CrCl ≥ 30 ml min−1. Daily daptomycin use up to 8 mg kg−1 doses are appropriate for patients on CVVHDF, but higher doses may increase the risk of toxicity.

SD-1077, a selectively deuterated precursor of dopamine (DA) structurally related to L-3,4-dihydroxyphenylalanine (L-DOPA), is under development for treatment of motor symptoms of Parkinson's disease. Preclinical models have shown slower metabolism of central deuterated DA. The present study investigated the peripheral pharmacokinetics (PK), metabolism and safety of SD-1077.Plasma and urine PK of drug and metabolites and safety after a single oral 150 mg SD-1077 dose were compared to 150 mg L-DOPA, each in combination with 37.5 mg carbidopa (CD) in a double-blind, two-period, crossover study in healthy volunteers (n = 16).Geometric least squares mean ratios (GMRs) and 90% confidence intervals (90% CI) of SD-1077 vs. L-DOPA for CSD-1077/CD demonstrated the potential to prolong exposure to central DA at comparable peripheral PK and safety to the reference L-DOPA/CD combination. A single dose of SD-1077 is safe for further clinical development in Parkinson's disease patients.

Alisporivir is a cyclophilin inhibitor with demonstrated in vitro and in vivo activity against hepatitis C 11 virus (HCV). We estimated antiviral effectiveness of alisporivir alone or in combination with 12 pegylated-Inteferon (peg-IFN) in 88 patients infected with different HCV genotypes treated for four 13 weeks. The pharmacokinetics of both drugs were modeled and used as driving functions for the viral 14 kinetic model. Genotype was found to significantly affect pegylated-Inteferon effectiveness (e= 86.3% 15 and 99.1% in genotype-1/4 and genotype-2/3, respectively, p

Alisporivir (ALV) is a cyclophilin inhibitor with pan-genotypic activity against hepatitis C virus (HCV). Here, we characterize the viral kinetics observed in 249 patients infected with HCV genotypes 2 or 3 and treated for 6 weeks with different doses of ALV with or without ribavirin (RBV). We use this model to predict the effects of treatment duration and different doses of ALV plus RBV on sustained virologic response (SVR). Continuous viral decline was observed in 214 (86%) patients that could be well described by the model. All doses led to a high level of antiviral effectiveness equal to 0.98, 0.96, and 0.90 in patients treated with 1,000, 800, and 600 mg of ALV once-daily, respectively. Patients that received RBV had a significantly faster rate of viral decline, which was attributed to an enhanced loss rate of infected cells, δ (mean δ = 0.35 d−1 vs. 0.21 d−1 in patients ± RBV, respectively; P = 0.0001). The remaining 35 patients (14%) had a suboptimal response with flat or increasing levels of HCV RNA after 1 week of treatment, which was associated with ALV monotherapy, high body weight, and low RBV levels in patients that received ALV plus RBV. Assuming full compliance and the same proportion of suboptimal responders, the model predicted 71% and 79% SVR after ALV 400 mg with RBV 400 mg twice-daily for 24 and 36 weeks, respectively. The model predicted that response-guided treatment could allow a reduction in mean treatment duration to 25.3 weeks and attain a 78.6% SVR rate. Conclusion: ALV plus RBV may represent an effective IFN-free treatment that is predicted to achieve high SVR rates in patients with HCV genotype 2 or 3 infection. (Hepatology 2014;59:1706–1714)

Relationships between tocilizumab exposure and response were evaluated using data from 4 phase III studies. Increased tocilizumab exposure was associated with improvements in Disease Activity Score using 28 joints (DAS28) and American College of Rheumatology (ACR) criteria and with a decrease in inflammation markers. A population pharmacokinetic/pharmacodynamic (PKPD) model was developed to describe data from 2 studies. An indirect-response model with a sigmoid Emax (maximal drug effect) inhibitory drug effect on DAS28 “production” rate adequately described the relationship between tocilizumab concentration and DAS28. Mean minimum serum tocilizumab concentration at steady state was greater than the EC50 (concentration at which 50% of Emax on DAS28 is reached) with the 8-mg/kg dose but not with the 4-mg/kgdose. Simulations within a large rheumatoid arthritis (RA) population showed that DAS remission rates were 38% for 8 mg/kg and 24% for 4 mg/kg. Tocilizumab was more potent in RA patients with higher baseline interleukin-6 levels, but this effect was not clinically significant. Other covariates (eg, presence of neutralizing antitocilizumab antibodies) did not demonstrate a clinically meaningful effect on tocilizumab DAS28 dose-response relationships. These data support clinical observations that tocilizumab 8 mg/kg is more effective than 4 mg/kg in reducing disease activity.

Aim The objective of this population pharmacokinetic (PK) analysis was to provide guidance for the dosing interval of daptomycin in patients undergoing continuous renal replacement therapy (CRRT). Methods A previously published population PK model for daptomycin was updated with data from patients undergoing continuous veno‐venous haemodialysis (CVVHD; n = 9) and continuous veno‐venous haemodiafiltration (CVVHDF; n = 8). Model‐based simulations were performed to compare the 24 h AUC, C max and C min of daptomycin following various dosing regimens (4, 6, 8, 10, and 12 mg kg−1 every [Q] 24 h and Q48 h), with the safety and efficacy exposure references for Staphylococcus aureus bacteraemia/right‐sided infective endocarditis. Results The previously developed daptomycin structural population PK model could reasonably describe data from the patients on CRRT. The clearance in patients undergoing CVVHDF and CVVHD was estimated at 0.53 and 0.94 l h−1, respectively, as compared with 0.75 l h−1 in patients with creatinine clearance (CrCl) ≥ 30 ml min−1. Daptomycin Q24 h dosing in patients undergoing CRRT resulted in optimal exposure for efficacy, with AUC comparable to that in patients with CrCl ≥ 30 ml min−1. In contrast, Q48 h dosing was associated with considerably lower AUC24–48h in all patients for doses up to 12 mg kg−1 and is therefore inappropriate. Conclusions Q24 h dosing of daptomycin up to 12 mg kg−1 provides comparable drug exposure in patients on CVVHD and in those with CrCl ≥ 30 ml min−1. Daily daptomycin use up to 8 mg kg−1 doses are appropriate for patients on CVVHDF, but higher doses may increase the risk of toxicity.

We present a mechanistic population model for the pharmacokinetics of nicotine (NIC), its primary (CYP2A6-generated) metabolite cotinine (COT), and COT's primary (CYP2A6-generated) metabolite, trans-3'-hydroxycotinine (3HC). Sixty-six subjects received oral deuterium-labeled NIC (NIC-d(2), 2 mg), and COT (COT-d(4), 10 mg) simultaneously. Frequent plasma/saliva samples were taken for measurement of concentrations of NIC-d(2), COT-d(2), 3HC-d(2), COT-d(4), and 3HC-d(4). A mechanistic population pharmacokinetic model was fitted to all data simultaneously. Most of the pharmacokinetic parameters found here agree with previous studies and with a previous model-independent analysis of these data. However, 3HC t(1/2) was found to be considerably shorter than a previously reported value, possibly because 3HC elimination was saturated with the larger doses used in the previous study. Additionally, the delay in the appearance of COT-d(2) in the blood was modeled as a time delay (t(1/2) = 12 min) in its release from the liver following NIC-d(2) administration. The most important result of the previous model-independent analysis of these data, confirmed here, is that NIC clearance to COT and the 3HC:COT saliva concentration ratio are highly correlated (r = 0.7-0.8). The correlation above support that idea that the 3HC:COT ratio can be used as a predictor of CYP2A6 activity and nicotine clearance. The model-based analysis extends and further justifies this conclusion.

IntroductionDeutetrabenazine is approved for treating Huntington disease (HD) chorea and is being evaluated for tardive dyskinesia (TD).ObjectiveTo assess the effect of deutetrabenazine on cardiac repolarization.MethodsA QT interval study was performed to evaluate effects of deutetrabenazine 12 and 24 mg on cardiac repolarization, as assessed by time-matched change from baseline, placebo-adjusted, in Fridericia-corrected QT interval (ΔΔQTcF). Moxifloxacin (400 mg) and tetrabenazine (50 mg) were the positive control and comparator, respectively. An exposure–response analysis was developed from this study to predict maximal effects on QTcF at maximum recommended dosing based on CYP2D6 status, an approach consistent with regulatory guidance at predicting QT interval effects.ResultsMaximal ΔΔQTcF between the least-squares mean (90% two-sided confidence interval) of deutetrabenazine 12 and 24 mg (n=45 in each group) were 2.8 (0.7–4.8) ms and 4.5 (2.4–6.5) ms, respectively. The ΔΔQTcF increase with tetrabenazine (n=45) was 7.6 (5.6–9.5) ms. Assay sensitivity was verified with moxifloxacin (n=47), which produced a maximal effect on ΔΔQTcF of 14.0 (11.9–16.0) ms. A linear model was developed that described a correlation between plasma concentrations from pivotal HD andTD trials (n=101) and QT interval prolongation. Using that model and the individual predicted Cmax for HD and TD patients, the placebo-adjusted change from baseline inQTcF for deutetrabenazine at maximal recommended daily doses was found to be 5.4 (2.5–9.5) ms.ConclusionsPatients receiving the maximal recommended doses of deutetrabenazine are predicted to have a QTcF increase below the level of regulatory concern.Presented at: Psych Congress; September 16–19, 2017; New Orleans, Louisiana, USA.Funding AcknowledgementsThis study was funded by Teva Pharmaceutical Industries, Petach Tikva, Israel

To estimate the effect of elevated serum homocysteine level on renal function decline and on the incidence of chronic kidney disease (CKD) in the general population.A historical prospective study on 3602 subjects attending a screening center in Israel between the years 2000 and 2012. Only subjects with normal estimated glomerular filtration rate (eGFR) and without proteinuria were included. Subjects were divided to two groups according to mean total serum homocysteine level (≤ 15,15μmol/l). Linear mixed effect model was used to estimate the annual eGRF decline in respect to homocysteine group. Cox proportional hazards models were used to estimate hazard ratios for CKD in the normal compared to the elevated homocysteine group.Annual eGFR decline was 25% higher in subjects with elevated versus normal mean homocysteine level (0.90 ± 0.16 ml/min/1.37 m(2) vs. 0.72 ± 0.14 ml/min/1.37 m(2), p0.001). In a median follow up of 7.75 years, 38 subjects developed CKD (1.05%). Elevated mean homocysteine level was highly associated with developing CKD (HR 4.85, 95% CI 2.48-9.49, p0.001). In a multivariate analysis which adjusted for age, baseline kidney function, HDL cholesterol, BMI, vitamin B12 and folic acid levels, these relationships remained substantially unchanged.Elevated mean serum homocysteine level is associated with an accelerated decline in renal function in both men and women, and is an independent risk factor for the development of CKD in the general population. Further prospective randomized clinical trials are needed to clarify whether the reduction in serum homocysteine concentrations will result in an improved renal prognosis.

Purpose. The purpose of this study was to evaluate the in vitro inhibitory potency of various amide analogues and derivatives of valproicacid toward human microsomal epoxide hydrolase (mEH).

Purpose. To explore the utilization of seven novel hydroxamic acid derivatives of valproic acid (VPA) as new antiepileptics.

Alisporivir (ALV) is a cyclophilin inhibitor with pan-genotypic activity against hepatitis C virus (HCV). Here, we characterize the viral kinetics observed in 249 patients infected with HCV genotypes 2 or 3 and treated for 6 weeks with different doses of ALV with or without ribavirin (RBV). We use this model to predict the effects of treatment duration and different doses of ALV plus RBV on sustained virologic response (SVR). Continuous viral decline was observed in 214 (86%) patients that could be well described by the model. All doses led to a high level of antiviral effectiveness equal to 0.98, 0.96, and 0.90 in patients treated with 1,000, 800, and 600 mg of ALV once-daily, respectively. Patients that received RBV had a significantly faster rate of viral decline, which was attributed to an enhanced loss rate of infected cells, δ (mean δ = 0.35 d(-1) vs. 0.21 d(-1) in patients ± RBV, respectively; P = 0.0001). The remaining 35 patients (14%) had a suboptimal response with flat or increasing levels of HCV RNA after 1 week of treatment, which was associated with ALV monotherapy, high body weight, and low RBV levels in patients that received ALV plus RBV. Assuming full compliance and the same proportion of suboptimal responders, the model predicted 71% and 79% SVR after ALV 400 mg with RBV 400 mg twice-daily for 24 and 36 weeks, respectively. The model predicted that response-guided treatment could allow a reduction in mean treatment duration to 25.3 weeks and attain a 78.6% SVR rate.ALV plus RBV may represent an effective IFN-free treatment that is predicted to achieve high SVR rates in patients with HCV genotype 2 or 3 infection.

The current paradigm for studying hepatitis C virus (HCV) dynamics in patients utilizes a standard viral dynamic model that keeps track of uninfected (target) cells, infected cells, and virus. The model does not account for the dynamics of intracellular viral replication, which is the major target of direct-acting antiviral agents (DAAs). Here we describe and study a recently developed multiscale age-structured model that explicitly considers the potential effects of DAAs on intracellular viral RNA production, degradation, and secretion as virus into the circulation. We show that when therapy significantly blocks both intracellular viral RNA production and virus secretion, the serum viral load decline has three phases, with slopes reflecting the rate of serum viral clearance, the rate of loss of intracellular viral RNA, and the rate of loss of intracellular replication templates and infected cells, respectively. We also derive analytical approximations of the multiscale model and use one of them to analyze data from patients treated for 14 days with the HCV protease inhibitor danoprevir. Analysis suggests that danoprevir significantly blocks intracellular viral production (with mean effectiveness 99.2%), enhances intracellular viral RNA degradation about 5-fold, and moderately inhibits viral secretion (with mean effectiveness 56%). The multiscale model can be used to study viral dynamics in patients treated with other DAAs and explore their mechanisms of action in treatment of hepatitis C., Author Summary Chronic infection with hepatitis C virus (HCV) remains an important health-care problem worldwide despite significant progress in the development of HCV therapy since the discovery of the virus in 1989. Current treatment options are focused on direct-acting antiviral agents (DAAs) that target specific steps of the HCV life cycle. Danoprevir, one of the DAAs that inhibit the HCV NS3-4A protease, has induced substantial viral load reductions in patients receiving therapy. We study the viral decline during therapy using a multiscale age-structured model that accounts for the dynamics of intracellular viral replication, and which includes the major steps in the HCV life cycle that are targeted by DAAs. We examine the biological parameters contributing to different phases of the viral decline after treatment initiation. We also explore the mechanisms of action of danoprevir and estimate its treatment effectiveness. The multiscale model provides a theoretical framework for studying virus dynamics in hepatitis C patients treated with other DAAs currently in clinical development, and may help one to optimally combine drugs with complementary modes of action to maximize the HCV cure rate.

Relationships between tocilizumab exposure and response were evaluated using data from 4 phase III studies. Increased tocilizumab exposure was associated with improvements in Disease Activity Score using 28 joints (DAS28) and American College of Rheumatology (ACR) criteria and with a decrease in inflammation markers. A population pharmacokinetic/pharmacodynamic (PKPD) model was developed to describe data from 2 studies. An indirect-response model with a sigmoid E(max) (maximal drug effect) inhibitory drug effect on DAS28 "production" rate adequately described the relationship between tocilizumab concentration and DAS28. Mean minimum serum tocilizumab concentration at steady state was greater than the EC(50) (concentration at which 50% of E(max) on DAS28 is reached) with the 8-mg/kg dose but not with the 4-mg/kgdose. Simulations within a large rheumatoid arthritis (RA) population showed that DAS remission rates were 38% for 8 mg/kg and 24% for 4 mg/kg. Tocilizumab was more potent in RA patients with higher baseline interleukin-6 levels, but this effect was not clinically significant. Other covariates (eg, presence of neutralizing antitocilizumab antibodies) did not demonstrate a clinically meaningful effect on tocilizumab DAS28 dose-response relationships. These data support clinical observations that tocilizumab 8 mg/kg is more effective than 4 mg/kg in reducing disease activity.

Relationships between tocilizumab exposure and response were evaluated using data from 4 phase III studies. Increased tocilizumab exposure was associated with improvements in Disease Activity Score using 28 joints (DAS28) and American College of Rheumatology (ACR) criteria and with a decrease in inflammation markers. A population pharmacokinetic/pharmacodynamic (PKPD) model was developed to describe data from 2 studies. An indirect-response model with a sigmoid E

Certain irregularities in calcium metabolism such as Paget's disease, osteoporosis, as well as osteolysis in bone cancer, are characterized by excessive destruction of the bone by resorption. In contrast, a number of clinically important diseases, for example, atherosclerosis, kidney and renal calculu8, arthritis, and bioprosthetic heart valve calcification are characterized by the deposition of calcium phosphate. nis~hosphonates are a relct3vely new class of drugs, that have been used in these diseases to inhibit both mineralization and bone resorption, following the recognition, that they are stable analogs of endogenous pyrophosphate, which is a physiological inhibitor of calcification and bone resorption. A number of geminal bisphosphonates, namely, Pamidronate (ABP), Etidronate (HEBP), and Clodronate (ClMBP), have been approved for clinical use.

Some geminal bisphosphonates are used clinically for a number of important bone/calcium related diseases; however, side effects and lack of selectivity impede their wide use. This work reports the synthesis and evaluation of bisacylphosphonates (e.g., adipoyl- and suberoylbisphosphonate). These compounds were found to inhibit significantly hydroxyapatite formation and dissolution in vitro and the calcification of bioprosthetic tissue implanted subdermally in rats. These are the first instances of nongeminal bisphosphonates [P–(C)n– P, n ≥ 2] that have been reported to be active in calcium-related disorders. The reported bisacylphosphonates possess apparent lower toxicity, and their calcium complexes/salts have improved solubility properties. Therefore, they are of potential importance for clinical applications.

To develop and compare methods that predict individual nicotine (NIC) clearance, which reflects CYP2A6 activity, using random saliva cotinine (COT) and trans 3′-hydroxycotinine (3HC) measurements. COT and 3HC saliva concentrations in smokers were simulated utilizing a mechanistic population pharmacokinetic model of NIC metabolism that was adapted from the one described in a companion paper. Four methods to predict NIC clearance using the metabolites concentrations were compared. The precision bias, and the fraction of predictions that are made with an absolute error below 25% were the performance measures evaluated. Four prediction methods were compared: (M1) reference method, an intercept slope model of the metabolite concentration ratios ([3HC]/[COT]) (M2) an intercept slope model of the natural logarithm of the metabolite ratios (M3) a spline of the logarithm of the metabolite ratios (M4) Maximal Posteriori Bayesian estimate of NIC clearance conditioned on the model, COT and 3HC concentrations. In addition, the effect of smoking patterns on the concentrations of COT and 3HC was evaluated. The precision, accuracy, and the fraction of predictions with an absolute error below 25%, were higher for methods M2–M4 compared to method M1. However, the differences between M2 and M4 were small. Additionally, smoking pattern did not affect the metabolite concentration profiles. Predicting NIC clearance using an intercept slope model of the natural logarithm of the ratio of 3HC to COT appears to be a relatively simple method that is better than using the metabolite ratio directly. This method has a bias of approximately −10%, precision of approximately 60%. The fraction of estimates below an absolute error of 25% is 43%. These results support use of M2 to estimate CYP2A6 activity in smokers in the clinical setting.

Purpose—Amifostine is a prodrug in which selectivity is largely determined by the preferential formation and uptake of its cytoprotective metabolite, WR-1065, in normal tissues as a result of differences in membrane-bound alkaline phosphatase activity. It was hypothesized that amifostine may be a good candidate for regional drug delivery to the liver because of its large hepatic extraction and total body clearance. Methods—Rat livers were implanted with Walker-256 tumors. The tumor-bearing rats received 15 min infusions of amifostine (200 mg/kg) via the portal vein or the femoral vein. WR-1065 concentrations in the blood, liver and tumor were measured at various times. Results—The WR-1065 tumor portal dosing AUC15−60 was 40% of systemic dosing, and tumor concentrations following portal dosing were one-fifth of that following systemic dosing. The portal dosing WR-1065 liver AUC15−60 was 60% higher than the values for systemic dosing. The liver/tumor concentration ratios of WR-1065 following portal dosing were up to 8-fold higher than the ratio following systemic administration. Unfortunately, systemic exposure to WR-1065 was greater following portal vs systemic amifostine. Conclusions—Amifostine may provide increased liver protection and decreased tumor protection from radio- or chemotherapy when administered by the portal vein. However, portal dosing also increases systemic exposure to WR-1065, which is associated with hypotension. Copyright © 2004 John Wiley & Sons, Ltd.

Amifostine is a prodrug in which selectivity is largely determined by the preferential formation and uptake of its cytoprotective metabolite, WR-1065, in normal tissues as a result of differences in membrane-bound alkaline phosphatase activity. In this study, we characterized the sites and extent of organ-specific activation by the liver, gastrointestinal tract, lungs, and kidneys after systemic administrations of amifostine. A total of 10 dogs were infused via the cephalic vein using sequential dose rates of drug at 0.125, 0.500, and 1.00 micro mol/min/kg. Infusion of each dose rate lasted 2 h, at which time steady-state plasma concentrations were obtained (i.e., portal vein, carotid artery, hepatic vein, pulmonary artery, and renal vein). The hepatic arterial, portal venous, and renal arterial blood flows, and cardiac output, were measured. The hepatic and splanchnic extraction of amifostine remained high at 90%, whereas gastrointestinal extraction decreased from 43 to 12 to 15% with increasing dose. Pulmonary extraction of amifostine was low at 7%, whereas renal extraction was intermediate at 57%. Because blood flow measurements were relatively constant during the drug infusions, clearance parameters paralleled that of organ extraction. As a result, saturability was observed in the gastrointestinal blood clearance (i.e., from 9.8 to 2.8-3.3 ml/min/kg) and total body plasma clearance of amifostine (i.e., from 52.6 to about 37.3 ml/min/kg), as the doses increased. Due to the drug's high activation in liver, these findings suggest that amifostine may offer good protection of this organ against the toxicities of chemotherapy and radiation.

Purpose: The tolerance of the liver to radiation is too low to permit an effective dose to be delivered to patients who have diffuse intrahepatic cancer. In this study we evaluated whether systemic or portal venous administration of the aminothiol compound, amifostine, could protect the normal liver from the effects of ionizing radiation without compromising tumor cell kill in a rat liver tumor model. Methods and Materials: Rats implanted with liver tumors were infused with 200 mg/kg amifostine over 15 min via the femoral or portal vein. The livers were irradiated with a single 6-Gy fraction 15–20 min after the termination of amifostine infusion. Protection of the liver was assessed by an in vitro hepatocyte micronucleus assay and tumor protection by an in vivo - in vitro clonogenic survival assay. Tissue levels of the active metabolite, free WR-1065, were determined in the tumor and in the normal liver using a specific HPLC assay with electrochemical detection. Results: After a 6-Gy fraction, the frequency of hepatocyte micronuclei after administration of saline, systemic amifostine, and portal venous amifostine was 18.7 ± 1%, 6.8 ± 1%, and 9.9 ± 2%, respectively, corresponding to a radiation equivalent effect of 6 Gy ± 0.5, 1.8 Gy ± 0.3, and 2.5 Gy ± 1.3, respectively. Both amifostine conditions showed considerably less radiation effect than saline-treated controls ( p p = 0.3). The surviving fraction of tumor cells was not affected by amifostine treatment and was 0.03 ± 0.02 and 0.05 ± 0.03 for systemic and portal venous delivery and 0.06 ± 0.02 for control animals (ANOVA analysis showed no significant difference of the means p = 0.34). Portal venous delivery produced significantly less WR-1065 in the tumor compared to systemic administration (54 μM ± 36 vs. 343 μM ± 88, respectively, p = 0.03). Conclusions: Both systemic and portal venous administration of amifostine effectively protect hepatocytes from ionizing radiation without compromising tumor cell kill in a clinically relevant animal model. These findings suggest that amifostine may be a selective normal tissue radioprotectant in liver cancer and that regional/portal infusions may be preferable to systemic dosing.

Hepatitis C viral kinetic analysis based on nonlinear mixed effect models can be used to individualize treatment. For that purpose, it is necessary to obtain precise estimation of individual parameters. Here, we evaluated by simulation the influence on Bayesian individual parameter estimation and outcome prediction of a priori information on population parameters, viral load sampling designs, and methods for handling data below detection limit (BDL). We found that a precise estimation of both individual parameters and treatment outcome could be obtained using as few as six measurements in the first month of therapy. This result remained valid even when incorrect a priori information on population parameters was set as long as the parameters were identifiable and BDL data were properly handled. However, setting wrong values for a priori population parameters could lead to severe estimation/prediction errors if BDL data were ignored and not properly accounted in the likelihood function. CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e56; doi:10.1038/psp.2013.31; published online 17 July 2013

The mean serum half life of rituximab reported in the current approved package insert (February 2007) is 76.3 and 205.8 hours following the first and fourth infusions, respectively. This results is based on data from 14 Non-Hodgkin’s Lymphoma (NHL) patients treated with a dose of 375 mg/m2 weekly × 4 analyzed using non-compartmental analysis (NCA). The aims of the current analysis were: to develop a population pharmacokinetic (POP PK) model using a large NHL patient population to investigate possible mechanisms that may explain the observed increase in half-life with time such as a B-cell/tumor burden mediated clearance to identify covariates as potential predictors of PK variability. The population PK analysis was performed using NONMEM V based on 3739 rituximab serum concentration samples from 298 patients who received rituximab as a single agent or in combination with cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) therapy from six clinical studies. Tested covariates evaluated included body surface area (BSA), gender, age, race, WHO status, baseline CD19+ counts, sum of the tumor perpendicular diameters (SPD) of tumor and CHOP therapy. A non-parametric bootstrap procedure was used to estimate the precision of model parameters, and the model performance was assessed using visual predictive check. Rituximab concentration data were best described by a two-compartment model with time-varying clearance. Total clearance comprised of two terms, a non-specific clearance pathway (CL1), which remains unchanged throughout treatment, and a specific clearance pathway (CL2, B cells/tumor burden mediated), which decreased at a first-order decay rate from its initial value following the first infusion. The typical population estimates of rituximab nonspecific clearance (CL1), specific clearance (CL2), and central compartment volume of distribution (V1) were 0.14 L/day, 0.59 L/day, and 2.7 L, respectively. Age, gender, race, and WHO performance status had no effect on the PK of rituximab. Covariate analysis revealed that patients with higher CD19 counts or SPD of tumor burden at baseline had a higher rituximab CL2, while V1 varied by body surface area (BSA) and CHOP chemotherapy. However, unexplained inter-individual variability remained high for CL2 following correction for CD19/SPD. Changes from typical V1 values contributed by extreme BSA (1.53 to 2.32 m2) and concurrent CHOP therapy, were relatively minor (27.1% and 19.0%) and explained 27.3% and 5.75% of the inter-individual variability in V1, respectively. Dose adjustment for the tested covariates is not expected to result in a meaningful reduction in rituximab PK variability. Retrospective analysis of rituximab PK using non linear mixed effect modeling confirmed that rituximab elimination decreased following multiple infusions. The median of individual estimates of rituximab terminal half-life was 22 days (range, 6.1 to 52 days), which is typical for immunoglobulin isotype IgG in human and is longer than that reported for humanized anti-CD20 clinical candidates, IMMU106 and of atumumab of 12.0 and 14.3 days, respectively.

The protease inhibitor (PI) RTV was used in ACTG359 as a metabolic inhibitor to increase saquinavir (SQV) concentrations, and also to contribute to virologic efficacy. HIV-positive patients (99) were administered SQV and RTV (both 400 mg bid). Intensive PK samples were taken from a subset (18) and random concentrations were obtained from all patients. A one-compartment disposition PK model with input via a catenary chain of four absorption compartments (a new modeling feature for this drug) was fit to the data. RTV pop PK parameters were estimated, as were MAP Bayes estimates of each individual's oral clearance (CL/F) and the ratio of the posterior variance of this estimate to its prior variance (PVR). This ratio is reciprocally proportional to the amount of information supplied by all PK observations in the individual. Pop PK estimates are: CL/F = 7.4 L/h, consistent with previous studies; volume of distribution = 59.7 L; mean absorption time = 3.25 h. The catenary chain absorption sub-model was necessary to fit the slow sigmoidal ascent to peak RTV concentration, and may prove useful in other cases of delayed peak concentrations of PIs. PVRs were considerably higher for individuals with only sparse samples than for those intensively sampled, providing a means to weight CL/F as a covariate for exposure-response regressions. Clinical Pharmacology & Therapeutics (2004) 75, P88–P88; doi: 10.1016/j.clpt.2003.11.335