Chemoprotective Antimalarial Activity of P218 against Plasmodium falciparum: A Randomized, Placebo-Controlled Volunteer Infection Study.

P218 is a highly selective dihydrofolate reductase inhibitor with potent in vitro activity against pyrimethamine-resistant Plasmodium falciparum. This single-center, randomized, double-blind, placebo-controlled phase Ib study evaluated P218 safety, pharmacokinetics, and chemoprotective efficacy in a P. falciparum sporozoite (PfSPZ) volunteer infection study (VIS). Consecutive dose safety and tolerability were evaluated (cohort 1), with participants receiving two oral doses of P218 1,000 mg 48 hours apart (n = 6), or placebo (n = 2). P218 chemoprotective efficacy was assessed (cohorts 2 and 3) with direct venous inoculation of 3,200 aseptic, cryopreserved PfSPZ (NF54 strain) followed 2 hours later with two P218 doses of 1,000 mg (cohort 2, n = 9) or 100 mg (cohort 3, n = 9) administered 48 hours apart, or placebo (n = 6). Parasitemia was assessed from day 7 using quantitative PCR targeting the var gene acidic terminal sequence (varATS qPCR). By day 28, all participants in cohort 2 (P218 1,000 mg) and 8/9 in cohort 3 (P218 100 mg) were sterilely protected post-PfSPZ VIS, confirming P218 P. falciparum chemoprotective activity. With placebo, all six participants became parasitemic (geometric mean time to positive parasitemia 10.6 days [90% CI: 9.9-11.4]). P218 pharmacokinetics were similar in participants with or without induced infection. Adverse events of any cause occurred in 45.8% (11/24) of participants who received P218 and 50.0% (4/8) following placebo; all were mild/moderate in severity, transient, and self-limiting. There were no clinically relevant changes in laboratory parameters, vital signs, or electrocardiograms. P218 displayed excellent chemoprotective efficacy against P. falciparum with favorable safety and tolerability.

Phase 2 multiple-dose study of an FcRn inhibitor, rozanolixizumab, in patients with primary immune thrombocytopenia.

Primary immune thrombocytopenia (ITP) is a predominantly immunoglobulin G (IgG)-autoantibody-mediated disease characterized by isolated thrombocytopenia. Rozanolixizumab, a subcutaneously infused humanized monoclonal anti-neonatal Fc receptor (FcRn) antibody, reduced serum IgG in healthy volunteers. In this phase 2, multicenter, open-label study, patients with persistent/chronic primary ITP received 1 to 5 once-weekly subcutaneous infusions of rozanolixizumab (cumulative doses, 15-21 mg/kg). Primary objectives were safety and tolerability, and secondary objectives were clinical efficacy (change in platelet count) and pharmacodynamic effect (change in IgG). In all, 51 (77.3%) of 66 patients reported 1 or more adverse events (AEs), all mild-to-moderate, most commonly headaches (26 [39.4%] of 66), of which 15 were treatment related. Four patients had serious AEs, but none were treatment related. No AEs resulted in discontinuation of the study drug. No serious infections occurred. Platelet counts of ≥50 × 109/L were achieved at least once at any time after multiple infusions (5 × 4, 3 × 7, or 2 × 10 mg/kg: 35.7%, 35.7%, and 45.5% of patients, respectively) or single infusions (15 or 20 mg/kg: 66.7% and 54.5% patients, respectively). Minimum mean IgG levels and maximum mean platelet counts both occurred by day 8 in the higher (15 and 20 mg/kg) single-dose cohorts and maximum platelet count occurred by day 11 onward in the multiple-dose cohorts. No clinically meaningful changes occurred in IgA, IgM, IgE, or albumin levels. In patients with persistent/chronic primary ITP, rozanolixizumab demonstrated a favorable safety profile and rapid, substantial platelet increases concordant with substantial IgG reductions, especially with single doses. By day 8, in the 15 and 20 mg/kg single-dose cohorts, >50% patients achieved clinically relevant platelet responses (≥50 × 109/L), coinciding with the lowest mean IgG levels. These data support phase 3 development of rozanolixizumab in persistent/chronic primary ITP. This trial was registered at www.clinicaltrials.gov as #NCT02718716.

Safety, Tolerability, Pharmacokinetics, and Antimalarial Activity of the Novel Plasmodium Phosphatidylinositol 4-Kinase Inhibitor MMV390048 in Healthy Volunteers.

MMV390048 is a novel antimalarial compound that inhibits Plasmodium phosphatidylinositol-4-kinase. The safety, tolerability, pharmacokinetic profile, and antimalarial activity of MMV390048 were determined in healthy volunteers in three separate studies. A first-in-human, double-blind, randomized, placebo-controlled, single-ascending-dose study was performed. Additionally, a volunteer infection study investigated the antimalarial activity of MMV390048 using the Plasmodium falciparum induced blood-stage malaria (IBSM) model. Due to the high pharmacokinetic variability with the powder-in-bottle formulation used in both of these studies, a third study was undertaken to select a tablet formulation of MMV390048 to take forward into future studies. MMV390048 was generally well tolerated when administered as a single oral dose up to 120 mg, with rapid absorption and a long elimination half-life. Twelve adverse events were considered to be potentially related to MMV390048 in the first-in-human study but with no obvious correlation between these and MMV390048 dose or exposure. Although antimalarial activity was evident in the IBSM study, rapid recrudescence occurred in most subjects after treatment with 20 mg MMV390048, a dose expected to be subtherapeutic. Reformulation of MMV390048 into two tablet formulations (tartaric acid and Syloid) resulted in significantly reduced intersubject pharmacokinetic variability. Overall, the results of this study suggest that MMV390048 is well tolerated in humans, and the pharmacokinetic properties of the compound indicate that it has the potential to be used for antimalarial prophylaxis or inclusion in a single-dose cure. MMV390048 is currently being tested in a phase 2a study in Ethiopian adults with acute, uncomplicated falciparum or vivax malaria monoinfection. (The three clinical trials described here were each registered with ClinicalTrials.gov as follows: first-in-human study, registration no. NCT02230579; IBSM study, registration no. NCT02281344; and formulation optimization study, registration no. NCT02554799.).

First-in-human clinical trial to assess the safety, tolerability and pharmacokinetics of P218, a novel candidate for malaria chemoprotection.

AIMS: This first-in-human clinical trial of P218, a novel dihydrofolate reductase inhibitor antimalarial candidate, assessed safety, tolerability, pharmacokinetics and food effects in healthy subjects. METHODS: The study consisted of two parts. Part A was a double-blind, randomized, placebo-controlled, parallel group, ascending dose study comprising seven fasted cohorts. Eight subjects/cohort were randomized (3:1) to receive either a single oral dose of P218 (10, 30, 100, 250, 500, 750 and 1000 mg) or placebo. Part B was an open-label, cross-over, fed/fasted cohort (eight subjects) that received a 250 mg single dose of P218 in two treatment periods. RESULTS: P218 was generally well tolerated across all doses; 21 treatment-emergent adverse events occurred in 15/64 subjects. Nine adverse events in five subjects, all of mild intensity, were judged drug related. No clinically relevant abnormalities in ECG, vital signs or laboratory tests changes were observed. P218 was rapidly absorbed, with Cmax achieved between 0.5 and 2 hours post dose. Plasma concentrations declined bi-exponentially with half-life values ranging from 3.1 to 6.7 hours (10 and 30 mg), increasing up to 8.9 to 19.6 hours (doses up to 1000 mg). Exposure values increased dose-proportionally between 100 and 1000 mg for P218 (parent) and three primary metabolites (P218 ß-acyl glucuronide, P218-OH and P218-OH ß-acyl glucuronide). Co-administration of P218 with food reduced Cmax by 35% and delayed absorption by 1 hour, with no significant impact on AUC. CONCLUSION: P218 displayed favourable safety, tolerability and pharmacokinetics. In view of its short half-life, a long-acting formulation will be needed for malaria chemoprotection.

The FcRn inhibitor rozanolixizumab reduces human serum IgG concentration: A randomized phase 1 study.

Pathogenic immunoglobulin G (IgG) autoantibodies characterize some human autoimmune diseases; their high concentration and long half-life are dependent on recycling by the neonatal Fc receptor (FcRn). Inhibition of FcRn is an attractive new treatment concept for IgG-mediated autoimmune diseases. Rozanolixizumab (UCB7665; CA170_01519.g57 IgG4P) is an anti-human FcRn monoclonal antibody. In cynomolgus monkeys, rozanolixizumab reduced IgG (maximum 75 to 90% by about day 10), was well tolerated, and did not increase risk of infection. We also report a first-in-human, randomized, double-blind, placebo-controlled, dose-escalating study of intravenous (IV) or subcutaneous (SC) rozanolixizumab in healthy subjects (NCT02220153). The primary objective was to evaluate safety and tolerability. Secondary objectives were assessment of rozanolixizumab pharmacokinetics and pharmacodynamics, including effects on circulating IgG concentrations. Forty-nine subjects were randomized to receive rozanolixizumab (n = 36) or placebo (n = 13) across six cohorts. The first three cohorts received IV doses, and the subsequent three cohorts received SC doses, of rozanolixizumab 1, 4, or 7 mg/kg (n = 6 for each cohort; plus n = 7 or 6 for placebo, respectively). The most frequent treatment-emergent adverse event [TEAE; headache, 14 of 36 (38.9%) subjects] was dose-dependent and more prominent after IV administration. Severe TEAEs occurred in four subjects, all in the highest-dose IV group [headache (n = 3) and back pain (n = 1)]. Rozanolixizumab pharmacokinetics demonstrated nonlinear increases with dose. There were sustained dose-dependent reductions in serum IgG concentrations (IV and SC rozanolixizumab). These data provide clinical evidence for the therapeutic potential of rozanolixizumab.

Pharmacokinetic interactions between lersivirine and zidovudine, tenofovir disoproxil fumarate/emtricitabine and abacavir/lamivudine.

BACKGROUND: To investigate pharmacokinetic interactions associated with coadministration of lersivirine with zidovudine, tenofovir disoproxil fumarate (DF)/emtricitabine (Truvada(®)) or abacavir/lamivudine (Epzicom(®)/Kivexa(®)). METHODS: Three Phase I, open, crossover studies with two (studies 1 and 3) or three (study 2) treatment periods were conducted in healthy individuals. In study 1, individuals received zidovudine and placebo or zidovudine and lersivirine on days 1-14. In study 2, individuals received lersivirine and tenofovir DF/emtricitabine, lersivirine and placebo or tenofovir DF/emtricitabine and placebo on days 1-10. In study 3, individuals received abacavir/lamivudine only in period 1 (5 days) and abacavir/lamivudine and lersivirine in period 2 (10 days). Blood samples were taken on days 1-14 (study 1) or day of final dose (studies 2 and 3) and analysed using high performance liquid chromatography/dual mass spectrometry. Pharmacokinetic parameters were calculated by standard non-compartmental methods. RESULTS: When coadministered with lersivirine, zidovudine exposure increased by 35%, and exposure of its metabolite zidovudine-glucuronide decreased by 19%. Following coadministration of lersivirine and tenofovir DF/emtricitabine, tenofovir exposure increased by 30%, and lersivirine exposure decreased by 12%. Coadministration of lersivirine and abacavir/lamivudine increased abacavir exposure by 27% and decreased lamivudine exposure by 8%. Adverse events were predominantly mild in these Phase I studies. CONCLUSIONS: Coadministration of lersivirine with zidovudine, tenofovir DF/emtricitabine or abacavir/lamivudine influenced the systemic exposure of all nucleoside reverse transcriptase inhibitor agents investigated (except for lamivudine; emtricitabine pharmacokinetics were not assessed). Changes were not considered clinically meaningful for zidovudine and abacavir. The clinical relevance of the effect on tenofovir pharmacokinetics is currently unknown.

The effect of lersivirine, a next-generation NNRTI, on the pharmacokinetics of midazolam and oral contraceptives in healthy subjects.

PURPOSE: Lersivirine is a next-generation non-nucleoside reverse transcriptase inhibitor (NNRTI) with a unique resistance profile that exhibits potent antiretroviral activity against wild-type human immunodeficiency virus and clinically relevant NNRTI-resistant strains. Results from in vitro and in vivo investigations suggest that lersivirine is a cytochrome P450 (CYP3A4) inducer that is metabolized by CYP3A4 and uridine diphosphate glucuronosyltransferase (UGT) 2B7. In order to formally assess the effects of lersivirine on CYP3A4 metabolism and/or glucuronidation, we performed studies aimed at investigating the effects of lersivirine co-administration on the pharmacokinetics (PK) of midazolam, ethinylestradiol and levonorgestrel. METHODS: Two drug-drug interaction studies were performed. Healthy subjects were co-administered (1) single dose midazolam, a prototypical CYP3A4 substrate, followed by 14 days of lersivirine twice daily with single dose midazolam on the final day of lersivirine dosing or (2) 10 days of once-daily (QD) lersivirine and QD oral contraceptives (OCs; ethinylestradiol and levonorgestrel), substrates for CYP3A4, UGT2B7, and/or P-glycoprotein. The effects of co-administration on the PK parameters of midazolam and OCs were assessed. RESULTS: At clinically relevant lersivirine doses (500-1,000 mg total daily dose), the mean plasma exposure of midazolam was reduced in a dose-dependent manner by 20-36 %. Co-administration of lersivirine 1,000 mg QD with OCs had minor PK effects, increasing ethinylestradiol exposure by 10 % and reducing levonorgestrel exposure by 13 %. CONCLUSIONS: These data further support previous observations that lersivirine is a weak CYP3A4 inducer, a weak inhibitor of glucuronidation, and a P-glycoprotein inhibitor. In both studies, lersivirine appeared to have a good safety and tolerability profile.

The pharmacokinetics of lersivirine (UK-453,061) and HIV-1 protease inhibitor coadministration in healthy subjects.

OBJECTIVE: Lersivirine (UK-453,061) is a next-generation nonnucleoside reverse transcriptase inhibitor, active against wild-type HIV-1 and several nonnucleoside reverse transcriptase inhibitor-resistant strains. Four studies evaluated the pharmacokinetic (PK) interactions between lersivirine and various HIV-1 protease inhibitors. METHODS: Four phase I trials were conducted to assess the PK of lersivirine when coadministered with lopinavir/ritonavir, darunavir/ritonavir, or atazanavir with/without ritonavir, and to examine the effects of lersivirine on the PK of atazanavir with/without ritonavir. PK data included the area under the plasma concentration-time profile from time zero to the end of the dosing interval (AUC24), maximum plasma concentration (Cmax), minimum plasma concentration (Cmin, C24, or Ctrough), and time to Cmax (Tmax). Safety was assessed by recording adverse events, vital signs, and laboratory data. RESULTS: Coadministration of lersivirine with lopinavir/ritonavir, darunavir/ritonavir, or atazanavir/ritonavir decreased mean plasma lersivirine AUC24 by 43%, 22%, and 19%, respectively. Atazanavir had no effect on lersivirine exposure, except for a 16% decrease in lersivirine C24. Lersivirine had no effect on atazanavir AUC24 or Cmax, although Ctrough was reduced by 18% in the absence of ritonavir. CONCLUSIONS: Lersivirine exposure was reduced when coadministered with ritonavir-boosted protease inhibitors; a dose adjustment may be warranted. Unboosted atazanavir had no effect on lersivirine exposure, except for a small decrease in lersivirine C24. Lersivirine had no effect on atazanavir (with/without ritonavir) exposure, except for a decrease in Ctrough. Caution should be applied when unboosted atazanavir is coadministered with lersivirine. Coadministration of lersivirine with lopinavir/ritonavir, darunavir/ritonavir, or atazanavir with/without ritonavir seems to be generally well tolerated.

Pharmacokinetic effects of coadministration of lersivirine with raltegravir or maraviroc in healthy subjects.

Lersivirine (UK-453,061) is a new nonnucleoside reverse transcriptase inhibitor currently being developed as a treatment for human immunodeficiency virus type 1 infection. Lersivirine shows potent activity against wild-type and clinically relevant drug-resistant strains. Previous studies have demonstrated that lersivirine is metabolized by glucuronidation via UGT2B7 and by cytochrome P450 3A4 (CYP3A4). Lersivirine is also a weak inducer of the CYP3A4 enzyme. Therefore, coadministered lersivirine could potentially affect the pharmacokinetics of maraviroc, a CCR5 antagonist metabolized by CYP3A4, and raltegravir, an integrase inhibitor metabolized by glucuronidation. Two open-label studies assessed the pharmacokinetics of raltegravir and of maraviroc when they were coadministered with lersivirine and the pharmacokinetics of lersivirine when it was coadministered with raltegravir. Minor, clinically nonsignificant effects on the pharmacokinetics of raltegravir coadministered with lersivirine were observed at steady state for raltegravir, with estimated mean changes of -15%, -29%, and +25% in the area under the concentration-time profile from time zero to the end of the dosing interval (AUC(tau)), maximum plasma concentration (C(max)), and concentration observed 12 h postdose (C(12)), respectively. There were no clinically relevant effects of steady-state raltegravir on lersivirine AUC(tau), C(max), or concentration observed 24 h postdose (C(24)) (estimated mean changes of -2 to +5%). Coadministration of lersivirine at steady state with maraviroc resulted in no clinically relevant effects on maraviroc AUC(tau), C(max), or C(12) (estimated mean changes of +3.4 to +8.6%). Lersivirine appeared to be generally well tolerated in these studies and appears to be suitable for coadministration with raltegravir or maraviroc without the need for dose modification.

Effects of ketoconazole and valproic acid on the pharmacokinetics of the next generation NNRTI, lersivirine (UK-453,061), in healthy adult subjects.

AIMS: To investigate the effect of inhibitors of cytochrome P450 (CYP) 3A4 and glucuronidation (UGT2B7) on the pharmacokinetics of lersivirine (UK-453,061), a next generation non-nucleoside reverse transcriptase inhibitor with a unique resistance profile, and to investigate the safety and tolerability of co-administration of lersivirine with these inhibitors. METHODS: Two open-label, randomized, placebo-controlled, crossover studies were conducted in healthy subjects. Study 1 investigated the effect of ketoconazole (400 mg once daily) on the pharmacokinetics of lersivirine (250 mg once daily). Subjects received ketoconazole 400 mg once daily or placebo on days 1-2 and received lersivirine 250 mg once daily and ketoconazole 400 mg once daily or placebo on days 3-9. Study 2 investigated the effect of valproic acid (VPA, sodium valproate, 1000 mg once daily) on the PK of lersivirine (500 mg once daily). On days 1-7, subjects received lersivirine 500 mg once daily plus either VPA 1000 mg or placebo. RESULTS: Compared with lersivirine alone, co-administration with ketoconazole increased the lersivirine mean area under the curve (AUC(0,24 h)) and maximum plasma concentration (C(max) ) by 82% (90% CI 74%, 91%) and 61% (90% CI 41%, 83%), respectively. VPA increased the mean lersivirine AUC(0,24 h) by 25% (90% CI 16%, 35%), with little effect on C(max) (2.5%, 90% CI -9%, 16%). There were no serious adverse events and no treatment-related discontinuations from either study. CONCLUSIONS: Inhibition of CYP3A4 and UGT2B7 by ketoconazole increased lersivirine exposure. Inhibition of UGT2B7-mediated glucuronidation by VPA had a modest effect on lersivirine exposure. Co-administration of lersivirine with either ketoconazole or VPA appeared to be well tolerated.

Variability in the population pharmacokinetics of isoniazid in South African tuberculosis patients.

AIM: This study was designed to characterize the population pharmacokinetics of isoniazid in South African pulmonary tuberculosis patients. METHODS: Concentration-time measurements obtained from 235 patients receiving oral doses of isoniazid as part of routine tuberculosis chemotherapy in two clinical studies were pooled and subjected to nonlinear mixed-effects analysis. RESULTS: A two-compartmental model, including first-order absorption and elimination with allometric scaling, was found to describe the observed dose-exposure relationship for oral isoniazid adequately. A mixture model was used to characterize dual rates of isoniazid elimination. Estimates of apparent clearance in slow and fast eliminators were 9.70 and 21.6 l h(-1) , respectively. The proportion of fast eliminators in the population was estimated to be 13.2%. Central volume of distribution was estimated to be 10% smaller in female patients and clearance was found to be 17% lower in patients with HIV. Variability in absorption rate (90%) was completely interoccasional in nature, whereas in relative bioavailability, interoccasional variability (8.4%) was lower than interindividual variability (26%). Oral doses, given once daily according to dosing policies at the time, were sufficient to reach therapeutic concentrations in the majority of the studied population, regardless of eliminator phenotype. Simulations suggested that current treatment guidelines (5 mg kg(-1) ) may be suboptimal in fast eliminators with low body weight. CONCLUSIONS: A population pharmacokinetic model was developed to characterize the highly variable pharmacokinetics of isoniazid in a South African pulmonary tuberculosis patient population. Current treatment guidelines may lead to underexposure in rapid isoniazid eliminators.

Safety and tolerability of lersivirine, a nonnucleoside reverse transcriptase inhibitor, during a 28-day, randomized, placebo-controlled, Phase I clinical study in healthy male volunteers.

BACKGROUND: Lersivirine is a nonnucleoside reverse transcriptase inhibitor undergoing clinical development for the treatment of HIV-1. OBJECTIVE: The goal of this study was to investigate the safety and tolerability of multiple oral doses of lersivirine administered to healthy male subjects to assist in the planning of longer term studies. METHODS: This was a randomized, double-blind, double-dummy, placebo-controlled, parallel-group, multicenter, Phase I clinical study in fasting, healthy male volunteers. Subjects were randomly assigned in a ratio of 7:7:4:4 to receive lersivirine 500 mg BID, lersivirine 750 mg once daily, efavirenz 600 mg once daily, or placebo once daily for 28 days. Safety and tolerability were assessed throughout the study by continuous collection of adverse events (AEs), including adverse drug reactions, illnesses with onset during the study, exacerbation of previous illnesses, and clinically significant changes in physical examination findings. Vital sign measurements and ECGs were performed at screening; on day 1 (predose and 2, 3, and 4 hours postdose); on days 7, 14, 21, and 28 (predose); at discharge; and at follow-up. Safety laboratory tests (including hematology, chemistry, and urinalysis) were performed at screening; days 0, 7, 14, 21, and 27; and at follow-up. RESULTS: Of the 66 healthy male subjects enrolled (age range, 21-51 years; body mass index, 18.1-29.9 kg/m(2)), 40 were white, 22 were Asian, 3 were black, and 1 was of mixed race. There were no clinically significant laboratory abnormalities, including changes in lipid profile, liver or renal function test results, or ECG findings. Overall, 86% (18/21) of subjects in the lersivirine 500-mg BID group, 81% (17/21) in the lersivirine 750-mg once-daily group, 92% (11/12) in the efavirenz 600-mg once-daily group, and 92% (11/12) in the placebo group experienced at least one treatment-related AE. Eight subjects were permanently discontinued from the study; 4 subjects in the efavirenz group (3 of whom participated in the trial at the Brussels study center) were permanently discontinued due to AEs considered to be treatment related. No subjects receiving lersivirine permanently discontinued the study due to treatment-related AEs, although one subject temporarily discontinued treatment. In addition, 4 subjects withdrew consent (2 subjects [1 of whom was at the Brussels study center] receiving lersivirine 750 mg once daily and 2 subjects [1 of whom was at the Brussels study center] receiving efavirenz). There were no deaths or serious AEs in any of the study groups. CONCLUSION: Lersivirine appeared to be well tolerated after 28 days of continuous dosing in this small, selected group of young, healthy male volunteers.

Translational pharmacokinetic-pharmacodynamic modelling; application to cardiovascular safety data for PF-00821385, a novel HIV agent.

AIM: To assess the translation of pharmacokinetic-pharmacodynamic (PK-PD) relationships for heart rate effects of PF-00821385 in dog and man. METHODS: Cardiovascular telemetric parameters and concentration data were available for animals receiving active doses (0.5-120 mg kg(-1), n= 4) or vehicle. PF-00821385 was administered to 24 volunteers and pharmacokinetic and vital signs data were collected. PK-PD models were fitted using nonlinear mixed effects. RESULTS: Compartmental models with linear absorption and clearance were used to describe pharmacokinetic disposition in animal and man. Diurnal variation in heart and pulse rate was best described with a single cosine function in both dog and man. Canine and human heart rate change were described by a linear model with free drug slope 1.76 bpm microM(-1)[95% confidence interval (CI) 1.17, 2.35] in the dog and 0.76 bpm microM(-1) (95% CI 0.54, 1.14) in man. CONCLUSIONS: The preclinical translational of concentration-response has been described and the potential for further interspecies extrapolation and optimization of clinical trial design is addressed.

Population pharmacokinetics of rifampin in pulmonary tuberculosis patients, including a semimechanistic model to describe variable absorption.

This article describes the population pharmacokinetics of rifampin in South African pulmonary tuberculosis patients. Three datasets containing 2,913 rifampin plasma concentration-time data points, collected from 261 South African pulmonary tuberculosis patients aged 18 to 72 years and weighing 28.5 to 85.5 kg and receiving regular daily treatment that included administration of rifampin (450 to 600 mg) for at least 10 days, were pooled. A compartmental pharmacokinetic model was developed using nonlinear mixed-effects modeling. Variability in the shape of the absorption curve was described using a flexible transit compartment model, in which a delay in the onset of absorption and a gradually changing absorption rate were modeled as the passage of drug through a chain of hypothetical compartments, ultimately reaching the absorption compartment. A previously described implementation was extended to allow its application to multiple-dosing data. The typical population estimate of oral clearance was 19.2 liters x h(-1), while the volume of distribution was estimated to be 53.2 liters. Interindividual variability was estimated to be 52.8% for clearance and 43.4% for volume of distribution. Interoccasional variability was estimated for CL/F (22.5%) and mean transit time during absorption (67.9%). The use of single-drug formulations was found to increase both the mean transit time (by 104%) and clearance (by 23.6%) relative to fixed-dose-combination use. A strong correlation between clearance and volume of distribution suggested substantial variability in bioavailability, which could have clinical implications, given the dependence of treatment effectiveness on exposure. The final model successfully described rifampin pharmacokinetics in the population studied and is suitable for simulation in this context.

Linking preclinical and clinical whole-body physiologically based pharmacokinetic models with prior distributions in NONMEM.

PURPOSE: The aim of this study was to evaluate the performance of the NONMEM prior functionality compared to a full Bayesian method when applied to population physiological models using diazepam as a case study. METHODS: Whole-body physiologically based pharmacokinetic (WBPBPK) models for diazepam were initially developed, tested and calibrated for rats and man using a full Bayesian analysis as implemented in WINBUGS: . The final models were implemented in NONMEM and the results from the two analyses compared in terms of parameter estimates, measures of parameter precision and run times. RESULTS: NONMEM population parameter estimates were in close agreement with those produced by the Bayesian analysis although there was a substantial shortening of run time for both the animal WBPBPK model (4.5 vs. 21 h) and human WBPBPK models (2 vs. 167 h). The adequacy of the model and the final parameter estimates were judged to be sufficient by the model's ability to describe individual tissue concentration-time profiles. The model provided a good overall description of the plasma concentration-time data in both rat and man with comparable parameter precision. A limited nonparametric bootstrap (n = 50) was performed to assess parameter sensitivity, bias and imprecision. No systematic bias was seen when comparing bootstrap means to final parameter estimates. CONCLUSIONS: The ease of implementation and reductions in run time hopefully provide a further step forward in allowing the wider use of these complex and information-rich models together with clinical data in the future.

Oral trimethoprim-sulphamethoxazole levels in stable HIV-infected children.

BACKGROUND: Effective treatment of Pneumocystis jiroveci pneumonia (PCP) requires therapeutic serum concentrations of 5-10 microg/ml trimethoprim (TMP); consequently intravenous trimethoprim-sulphamethoxazole (TMP-SMZ) is recommended therapy. However, oral therapy is desirable as the intravenous route is costly, time-consuming, more difficult to administer and carries a risk of needlestick injury. OBJECTIVE: To investigate whether therapeutic TMP levels for treatment of PCP can be attained with oral therapy in HIV-infected children. METHODS: A prospective dose-escalation study was undertaken of serum TMP levels attained following oral doses of TMP of 5 mg/kg, 10 mg/kg or 20 mg/kg in stable HIV-infected children. Children who received a 20 mg/kg dose were randomised to get a second dose (5 or 10 mg/kg TMP) at 6 hours. TMP levels were measured at baseline, peak (3 hours), and trough (6 hours) using liquid chromatography. An additional TMP level was taken at 9 hours in those who received a second TMP dose. RESULTS: Median (25th-75th percentile) peak serum TMP levels following a 5 mg/kg, 10 mg/kg or 20 mg/kg oral loading dose were 0.93 (0.5-1.5) microg/ml, 1.94 (1.4-2.2) microg/ml and 7.68 (6.1-7.8) microg/ml respectively. Peak TMP levels at 9 hours after a second TMP dose of 5 or 10 mg/kg were 6.98 (3.4-8.8) microg/ml and 9.25 (8.2-10.3) microg/ml respectively. CONCLUSION: Therapeutic concentrations of TMP for treatment of P. jiroveci can be attained with an oral loading dose of 20 mg/kg and sustained with a second dose at 6 hours of either 5 mg or 10 mg/kg in stable HIV-infected children.

Variability in the population pharmacokinetics of pyrazinamide in South African tuberculosis patients.

OBJECTIVE: This study was designed to characterize the population pharmacokinetics of pyrazinamide in South African pulmonary tuberculosis patients, with special reference to interindividual and interoccasional variability (IIV and IOV, respectively). METHODS: Concentration-time measurements obtained from 227 patients receiving oral doses of pyrazinamide were pooled to create a dataset containing 3,092 data points spanning multiple dosing occasions. The software program NONMEM was used to analyze the data. RESULTS: A one-compartment model with first-order absorption, including a zero-order component describing release from formulation, and first-order elimination best described the data. The absorption rate constant was estimated to be bimodally distributed between two distinct subgroups, fast and slow, in approximately even proportion. Absorption rate was threefold greater in fast absorbers (3.56 h(-1)) in comparison to slow absorbers (1.25 h(-1)). Typical values of oral clearance and apparent volume of distribution were estimated as 3.42 L h(-1) and 29.2 l, respectively. IOV was supported in oral clearance (0.0238, variance) and absorption rate (0.623, variance). The duration of zero-order absorption was estimated as 0.290 h, and was quite variable between patients (0.957, variance). CONCLUSION: The absorption of pyrazinamide in the studied population was highly variable and two separate subpopulations were identified. IOV accounted for a proportion of the variability in clearance and the absorption rate constant.

Population pharmacokinetics of rifapentine and its primary desacetyl metabolite in South African tuberculosis patients.

This study was designed to describe the population pharmacokinetics of rifapentine (RFP) and 25-desacetyl RFP in a South African pulmonary tuberculosis patient population. Special reference was made to studying the influence of previous exposure to rifampin (RIF) and the variability in pharmacokinetic parameters between patients and between occasions and the influence of different covariates. Patients were included in the study if they had been receiving first-line antimycobacterial therapy (rifampin, isoniazid, pyrazinamide, and ethambutol) for not less than 4 weeks and not more than 6 weeks and were divided into three RFP dosage groups based on weight: 600 mg, <45 kg; 750 mg, 46 to 55 kg; and 900 mg, >55 kg. Participants received a single oral dose of RFP together with concomitant antimycobacterial agents, excluding RIF, on study days 1 and 5 after they ingested a soup-based meal. The RFP and 25-desacetyl RFP concentration-time data were analyzed by nonlinear mixed-effect modeling using NONMEM. The pharmacokinetics of the parent drug were modeled separately, and the individual pharmacokinetic parameters were used as inputs for the 25-desacetyl RFP pharmacokinetic model. A one-compartment disposition model was found to best describe the data for both the parent and the metabolite, and the metabolite was assumed to be formed only from the central compartment of the parent drug. Prior treatment with RIF did not alter the pharmacokinetics of RFP but appeared to increase the excretion of 25-desacetyl RFP in a nonlinear fashion. The RFP oral clearance and volume of distribution were found to increase by 0.049 liter/h and 0.691 liter, respectively, with a 1-kg increase from the median weight of 50 kg. The oral clearance of 25-desacetyl RFP was found to be 35% lower in female patients. The model developed here describes the population pharmacokinetics of RFP and its primary metabolite in tuberculosis patients and includes the effects of prior administration with RIF and covariate factors.

Structure of a helically extended SH3 domain of the T cell adapter protein ADAP.

The adapter protein ADAP (FYB/SLAP-130) provides a critical link between T cell receptor (TCR) signaling and cell adhesion via the activation of integrins. The C-terminal 70 residues of ADAP show homology to SH3 domains; however, conserved residues of the fold are absent. An alignment and annotation of this domain has therefore been elusive. We have solved the three-dimensional structure of the ADAP C-terminal domain by NMR spectroscopy and show that it represents an altered SH3 domain fold. An N-terminal, amphipathic helix makes extensive contacts to residues of the regular SH3 domain fold, and thereby a composite surface with unusual surface properties is created. We propose this SH3 domain variant to be classified as a helically extended SH3 domain (hSH3 domain) and show that the ADAP-hSH3 domain can no longer bind conventional proline-rich peptides.