Final Population Pharmacokinetic Model Research Articles

Pharmacokinetics of single-agent axitinib across multiple solid tumor types.

Axitinib, a potent and selective inhibitor of vascular endothelial growth factor receptors, showed antitumor activity as a single agent against several solid tumor types in Phase II and III trials. This study was conducted to evaluate axitinib pharmacokinetics across a variety of solid tumors. The current study analyzed the pharmacokinetics of axitinib in 110 patients with non-small cell lung cancer (NSCLC), thyroid cancer, or melanoma from three Phase II trials plus 127 healthy volunteers, using nonlinear mixed-effects modeling. Boxplots of maximum observed plasma concentration (C max) and area under the plasma concentration-time curve (AUC) of data from these tumor populations was compared to C max and AUC from the final population pharmacokinetic model developed for metastatic renal cell carcinoma (mRCC) to compare axitinib pharmacokinetics across different tumor types. Axitinib disposition based on data from 237 subjects was best described using a two-compartment model with first-order absorption and lag time. Population estimates for systemic clearance, central volume of distribution, absorption rate constant, absolute bioavailability, and lag time were 20.1L/h, 56.2L, 1.26/h(-1), 0.663, and 0.448h, respectively. Statistically significant covariates included gender on clearance, and body weight on central volume of distribution. However, predicted changes due to gender and body weight were found not clinically meaningful. The final analysis indicated that the pharmacokinetic model for mRCC was able to successfully describe axitinib pharmacokinetics in patients with NSCLC, thyroid cancer, and melanoma. The pharmacokinetics of axitinib appears to be similar across a variety of tumor types.

O-107 Prospective Validation Of A Model-based Dosing Regimen For Amikacin In Preterm And Term Neonates

<h3>Background and aims</h3> An essential step in drug dosing optimalisation is prospective validation of newly proposed dosing regimens. Based on a recently published population pharmacokinetic (PK) model, a neonatal amikacin dosing regimen was developed. The aim of the current study was to prospectively validate this model-derived dosing regimen. <h3>Methods</h3> Routine amikacin therapeutic drug monitoring (TDM) concentrations were prospectively collected. To test efficacy of the dosing regimen, early observed TDM results (i.e. prior to and 1 h after the second intravenous amikacin dose) reaching target concentrations (trough &lt;3 mg/L, peak &gt;24 mg/L) were defined. To test stability and accuracy of the model, all observed concentrations were compared with the predicted concentrations and a normalised prediction distribution error (NPDE) was performed. Monte Carlo simulations were used to evaluate amikacin exposure. <h3>Results</h3> In total, 1195 TDM results of 579 neonates [median gestational age 34 (range 24–41) weeks, postnatal age 2 (range 1–30) days] were included. Sixty percent of the early trough levels was below 3 mg/L, 90.4% of the peak levels reached 24 mg/L. Comparable parameter estimates were obtained between the final PK model and the prospective dataset. No trend was seen in the NPDE <i>versus</i> time and the NPDE <i>versus</i> predicted concentrations. Based on the Monte Carlo simulations, peak concentrations above 24 mg/L were reached in almost all patient subgroups. <h3>Conclusions</h3> After 14 years experience of amikacin dosing optimalisation in (pre)term neonates, a model-based dosing algorithm was prospectively validated confirming its efficacy, stability and accuracy over the entire neonatal population.

Bayesian approach for the estimation of cyclosporine area under the curve using limited sampling strategies in pediatric hematopoietic stem cell transplantation.

BackgroundThe optimal marker for cyclosporine (CsA) monitoring in transplantation patients remains controversial. However, there is a growing interest in the use of the area under the concentration-time curve (AUC), particularly for cyclosporine dose adjustment in pediatric hematopoietic stem cell transplantation. In this paper, we develop Bayesian limited sampling strategies (B-LSS) for cyclosporine AUC estimation using population pharmacokinetic (Pop-PK) models and investigate related issues, with the aim to improve B-LSS prediction performance.MethodsTwenty five pediatric hematopoietic stem cell transplantation patients receiving intravenous and oral cyclosporine were investigated. Pop-PK analyses were carried out and the predictive performance of B-LSS was evaluated using the final Pop-PK model and several related ones. The performance of B-LSS when targeting different versions of AUC was also discussed.ResultsA two-compartment structure model with a lag time and a combined additive and proportional error is retained. The final covariate model does not improve the B-LSS prediction performance. The best performing models for intravenous and oral cyclosporine are the structure ones with combined and additive error, respectively. Twelve B-LSS, consisting of 4 or less sampling points obtained within 4 hours post-dose, predict AUC with 95th percentile of the absolute values of relative prediction errors of 20% or less. Moreover, B-LSS perform better for the prediction of the ‘underlying’ AUC derived from the Pop-PK model estimated concentrations that exclude the residual errors, in comparison to their prediction of the observed AUC directly calculated using measured concentrations.ConclusionsB-LSS can adequately estimate cyclosporine AUC. However, B-LSS performance is not perfectly in line with the standard Pop-PK model selection criteria; hence the final model might not be ideal for AUC prediction purpose. Therefore, for B-LSS application, Pop-PK model diagnostic criteria should additionally account for AUC prediction errors.

Population pharmacokinetics of oxcarbazepine active metabolite in Chinese children with epilepsy.

This study was to establish the population pharmacokinetic (PPK) model of pharmacologically active metabolite of oxcarbazepine (OXC) and to estimate PPK parameters for the optimal individuation administration of OXC in Chinese children with epilepsy. The pharmacologically active metabolite, 10-monohydroxy derivative of OXC (MHD)was used as the analytical target for monitoring therapy of OXC. A total of 840 MHD serum samples from 466 children with epilepsy were analyzed using high-performance liquid chromatography with UV detection. Patients' clinical data were retrospectively collected. Population pharmacokinetics analysis was performed using a non-linear mixed-effect model with Phoenix NLME 1.2. Pharmacokinetic parameters were estimated according to a one-compartment model with first-order absorption and elimination. Effects of age,gender, total body weight (TBW), daily doseper weight (DDPW) and use of concomitant antiepileptic drugs (AEDs) were analyzed.Bootstrap and predictive check were used simultaneously to validate the final population pharmacokinetics models. The final PPK model of MHD was: Ka = 0.645 h⁻¹, V(L) = (11.3 + (age - 90.5) x 0.0282 + (TBW - 25.0) x 0.402) x e(0.0689), CL (L/h) = (0.557 + (DDPW - 20.8) x 0.00367 + (gender) x (-0.0636)) x e(0.120). The final PPK model was demonstrated to be suitable and effective by the bootstrap and predictive check. A PPK model of MHD in Chinese children with epilepsy was successfully established. PPK parameters of MHD could be predicted accurately by this model. This model may be very useful for establishing individual dosage guidelines of OXC in Chinese children with epilepsy.

Population pharmacokinetics of intravenous moxifloxacin 400 mg once-daily dosage in infected patients.

The purpose of this study was to explore the population pharmacokinetic features of moxifloxacin in infected patients. A total of 37 Chinese adult infected patients were treated with intravenous moxifloxacin (400mg/day). In total, 67 plasma samples of moxifloxacin were collected immediately after intravenous dripping and before administration on the 3rd, 4th or 5th day. A nonlinear mixed effect model was used to model the population pharmacokinetic (PK) behavior of moxifloxacin. The final population pharmacokinetic models were validated using the bootstrap method. Some covariates, including demographic characteristics and hematological and biological indicators, were analyzed. A structural model was developed based on a one-compartment model with intravenous infusion and first-order elimination. The typical population values of moxifloxacin for the pharmacokinetic parameters of apparent clearance (CL) and apparent distribution volume (V) were 12.9L/h and 115L, respectively. The inter-individual variabilities of CL and V were 36% and 28%, respectively. The covariates of WT influenced the CL and V values determined by the final model. The present study developed population pharmacokinetic models for moxifloxacin in infected Chinese patients. The results detailed here could provide a reference for individualized moxifloxacin therapy in the clinical setting.

Mo1228 Fecal Microbiota Transplantation Induces Early Improvement in Symptoms in Patients With Active Crohn's Disease

Background: Vedolizumab (VDZ), currently in development for treating ulcerative colitis (UC) and Crohn's disease (CD), exhibits target-mediated drug disposition. Described here are a VDZ population pharmacokinetic (PK) model, an estimation of typical VDZ parameter values, and effects of covariates that may be predictors of VDZ PK variability. Methods: The population PK data set included data from 5 VDZ clinical studies (1 phase 1 study in healthy subjects and 1 phase 2 study and 3 phase 3 studies [GEMINI 1, 2, and 3] in UC or CD patients). Analysis of repeatedmeasures was conducted via nonlinear mixed-effects modeling, using NONMEM (Version 7.2). The population PK base model was developed using firstorder conditional estimation with an η-e interaction method and extensively sampled phase 1 and 2 data. Results from the base model were used to develop the full covariate model, which was fit to sparse phase 3 data using the full Bayesian Markov Chain Monte Carlo method. Model selection was based on standard goodness-of-fit criteria. A full covariate modeling approach, emphasizing parameter estimation rather than stepwise hypothesis testing, was implemented for the population PK analysis. Results: The data set comprised 2554 individuals with 18,427 evaluable VDZ serum concentrations. VDZ PK was best described by a 2-compartmentmodel with parallel linear and nonlinear elimination. Reference covariates for the final PK model included baseline age, weight, albumin, disease activity scores (Crohn's Disease Activity Index score [CD]; partial Mayo Clinic score [UC]), prior anti-tumor necrosis factor α treatment, and inflammatory bowel disease diagnosis (CD or UC). Presence of anti-VDZ antibodies and use of adjuvant therapy (immunomodulator or aminosalicylate) were also evaluated. Overall, PK parameter estimates for patients with UC and CD were similar using reference values for individual covariates. At steady state, VDZ half-life estimate was 25 days for the linear elimination phase. Linear clearance of VDZ (CLL) was 0.159 L/day for UC and 0.155 L/day for CD. Volume of distribution for the central compartment (Vc) was 3.19 L and 1.66 L for the peripheral compartment. Interindividual variabilities (coefficients of variation) in CLL and Vc were 35% and 19%, respectively; proportional residual variance estimate was 24%. While baseline albumin had the potential to have a clinically relevant effect on VDZ CLL, defined as an effect size of more than ±25% from the reference value, effects of other covariates tested were not considered clinically meaningful. Conclusions: Population PK parameters were similar in patients with UC and CD. No change in dosing recommendations is needed based on baseline covariates (eg, age, gender, weight, presence of anti-VDZ antibodies, and albumin).

Modeling and simulation of bone mineral density response from a phase 2 study of ONO‐5334, a new cathepsin K inhibitor, to support dose selection in osteoporosis

ONO-5334, a selective inhibitor of cathepsin K, is a potential new treatment for osteoporosis. The objectives of this modeling study were to (1) develop exposure-response (E-R) models to relate ONO-5334 exposure to bone mineral density (BMD), (2) predict BMD responses to various doses of ONO-5334 for both immediate release tablet (IRT) and sustained release tablet (SRT) formulations where only BMD response after administration of IRT had been studied to date, (3) inform selection of appropriate formulation/dose using simulation for future clinical trials. A population pharmacokinetic (PK) model was developed to simultaneously analyze data for both IRT and SRT. The exposure metrics at steady state were estimated by post hoc Bayesian prediction using the final population PK model. E-R models were developed using dose-ranging data with only IRT from postmenopausal females with osteoporosis. Based on the developed model, lumbar spine and total hip BMD after administration of ONO-5334 SRT as well as IRT were simulated. The simulation results showed that ONO-5334 SRT should provide comparable BMD responses at a lower dose relative to IRT (a finding consistent with the results from a previous population PK-PD modeling study with bone resorption markers).

P530 Comparison between liposomial iron and ferrous sulfate in patients with iron deficiency anemia and inflammatory bowel disease. A pilot controlled study

Background: Vedolizumab (VDZ), currently in development for treating ulcerative colitis (UC) and Crohn's disease (CD), exhibits target-mediated drug disposition. Described here are a VDZ population pharmacokinetic (PK) model, an estimation of typical VDZ parameter values, and effects of covariates that may be predictors of VDZ PK variability. Methods: The population PK data set included data from 5 VDZ clinical studies (1 phase 1 study in healthy subjects and 1 phase 2 study and 3 phase 3 studies [GEMINI 1, 2, and 3] in UC or CD patients). Analysis of repeatedmeasures was conducted via nonlinear mixed-effects modeling, using NONMEM (Version 7.2). The population PK base model was developed using firstorder conditional estimation with an η-e interaction method and extensively sampled phase 1 and 2 data. Results from the base model were used to develop the full covariate model, which was fit to sparse phase 3 data using the full Bayesian Markov Chain Monte Carlo method. Model selection was based on standard goodness-of-fit criteria. A full covariate modeling approach, emphasizing parameter estimation rather than stepwise hypothesis testing, was implemented for the population PK analysis. Results: The data set comprised 2554 individuals with 18,427 evaluable VDZ serum concentrations. VDZ PK was best described by a 2-compartmentmodel with parallel linear and nonlinear elimination. Reference covariates for the final PK model included baseline age, weight, albumin, disease activity scores (Crohn's Disease Activity Index score [CD]; partial Mayo Clinic score [UC]), prior anti-tumor necrosis factor α treatment, and inflammatory bowel disease diagnosis (CD or UC). Presence of anti-VDZ antibodies and use of adjuvant therapy (immunomodulator or aminosalicylate) were also evaluated. Overall, PK parameter estimates for patients with UC and CD were similar using reference values for individual covariates. At steady state, VDZ half-life estimate was 25 days for the linear elimination phase. Linear clearance of VDZ (CLL) was 0.159 L/day for UC and 0.155 L/day for CD. Volume of distribution for the central compartment (Vc) was 3.19 L and 1.66 L for the peripheral compartment. Interindividual variabilities (coefficients of variation) in CLL and Vc were 35% and 19%, respectively; proportional residual variance estimate was 24%. While baseline albumin had the potential to have a clinically relevant effect on VDZ CLL, defined as an effect size of more than ±25% from the reference value, effects of other covariates tested were not considered clinically meaningful. Conclusions: Population PK parameters were similar in patients with UC and CD. No change in dosing recommendations is needed based on baseline covariates (eg, age, gender, weight, presence of anti-VDZ antibodies, and albumin).

Population pharmacokinetics of TC‐5214, a nicotinic channel modulator, in phase I and II clinical studies

TC-5214 (dexmecamylamine) is a nicotinic channel modulator that has previously been evaluated for treatment of major depression disorder (MDD) and is currently being evaluated by Targacept as a treatment for overactive bladder. A comprehensive population pharmacokinetic (POP PK) model of TC-5214 was developed using nonlinear mixed-effects modeling of pooled plasma concentration data from 6 early phase I studies in 179 healthy participants or patients with non-MDD and 1 phase II study in 68 MDD patients. Concentration-time profiles of TC-5214 after either single or multiple oral doses of TC-5214 was described by a one-compartment model with first-order absorption with lag time and first-order elimination. Covariate analysis revealed that creatinine clearance was a significant covariate on clearance and that body weight significantly influenced the central volume of distribution. The final model (with identified covariates) was used to simulate steady-state exposure for patients with impaired renal function. Results from forest plots reveal that patients with moderate to severe renal impairment or end stage renal disease are associated with significantly higher Cssmax and AUC compared to patients with normal renal function. The proposed final POP PK model could be employed in defining a TC-5214 dosage regimen in patients with impaired renal function.

Genetic algorithm guided population pharmacokinetic model development for simvastatin, concurrently or non-concurrently co-administered with amlodipine

An automated model development was performed for simvastatin, co-administered with amlodipine concurrently or non-concurrently (i.e., 4 hours later) in 17 patients with coexisting hyperlipidemia and hypertension. The single objective hybrid genetic algorithm (SOHGA) was implemented in the NONMEM software by defining the search space for structural, statistical and covariate models. Candidate models obtained from the SOHGA runs were further assessed for biological plausibility and the precision of parameter estimates, followed by traditional backward elimination process for model refinement. The final population pharmacokinetic model shows that the elimination rate constant for simvastatin acid, the active form by hydrolysis of its lactone prodrug (i.e., simvastatin), is only 44% in the concurrent amlodipine administration group compared with the non-concurrent group. The application of SOHGA for automated model selection, combined with traditional model selection strategies, appears to save time for model development, which also can generate new hypotheses that are biologically more plausible.

Population Pharmacokinetic Analysis of Linezolid in Low Body Weight Patients with Renal Dysfunction

Linezolid has antibacterial activity against aerobic Gram-positive cocci, including methicillin-resistant Staphylococcus aureus (MRSA). Adjustment of the dose of linezolid has been proposed to be unnecessary in patients with reduced renal function. However, platelet counts and hemoglobin levels were shown to be significantly lower in such patients than in patients with normal renal function. The population pharmacokinetic (PPK) of linezolid was investigated in MRSA infected patients with renal dysfunction. Linezolid concentrations in serum were measured by high-performance liquid chromatography. PPK analysis was performed in the nonlinear mixed effects model (NONMEM) computer program. In the final PPK model, total body weight (TBW), estimated glomerular filtration rate (eGFR), hemoglobin (HB), and alanine amino transferase (ALT) were influential covariates on total body clearance (CL), and the volume of distribution (Vd) was affected by TBW, which was expressed as CL (L/h) = 0.00327 × TBW × eGFR(0.428) × HB(0.502) × 0.283 (ALT ≥ 100 IU/L) and CL (L/h) = 0.00327 × TBW × eGFR(0.428) × HB(0.502) (ALT < 100 IU/L), Vd (L) = 1.310 × TBW. The PPK parameters of linezolid obtained here are useful for the optimal use of linezolid with similar patient population characteristics.

Population pharmacokinetic and pharmacodynamic analyses of teicoplanin in Japanese patients with systemic MRSA infection

Teicoplanin is a glycopeptide antibiotic used for the treatment of MRSA infection. An initial loading dose of 400 mg every 12 hours for three doses is the standard dosing regimen. This study aimed to assess whether this regimen was appropriate based on the pharmacokinetic/pharmacodynamic (PK/PD) analyses in Japanese patients. We conducted a population pharmacokinetic (PPK) analysis of teicoplanin by NONMEM using serum drug concentrations obtained from 116 patients with MRSA infection. PD of the drug was analyzed by a model assuming that the variability of therapeutic responses (assessed by body temperature, serum C-reactive protein concentrations, and white blood cell counts) on the 3rd, 7th or 14th day of treatment is associated with the logarithm of serum unbound drug concentration (Cmax,unbound) divided by the MIC against MRSA (log[Cmax,unbound/MIC]). The final PPK model showed that creatinine clearance and serum albumin concentration were significant (p < 0.01) covariates of systemic clearance and peripheral volume of distribution of teicoplanin, respectively. The PD analyses indicated that log[Cmax,unbound/MIC] of 0.30 on Day 3 of teicoplanin therapy was the threshold for achieving successful clinical responses. Integrating the PK and PD data, we consider that the standard loading dose regimen would attain the threshold serum level within the initial 3 days in only less than 50% of the patients. We propose that an extended loading regimen (400 mg every 12 hours for the first 5 doses) would be a treatment option to maximize the therapeutic effects of teicoplanin in patients with systemic MRSA infection.

Population Pharmacokinetics of Escalating Doses of Caspofungin in a Phase II Study of Patients with Invasive Aspergillosis

Caspofungin (CAS) is approved for second-line management of proven or probable invasive aspergillosis at a dose of 50 mg once daily (QD). Preclinical and limited clinical data support the concept of the dose-dependent antifungal efficacy of CAS with preservation of its favorable safety profile. Little is known, however, about the pharmacokinetics (PKs) of higher doses of CAS in patients. In a formal multicenter phase II dose-escalation study, CAS was administered as a 2-h infusion at doses ranging from 70 to 200 mg QD. CAS PK sampling (n = 468 samples) was performed on day 1 and at peak and trough time points on days 4, 7, 14, and 28 (70 mg, n = 9 patients; 100 mg, n = 8 patients; 150 mg, n = 9 patients; 200 mg, n = 20 patients; total, n = 46 patients). Drug concentrations in plasma were measured by liquid chromatography tandem mass spectroscopy. Population pharmacokinetic analysis (PopPK) was performed using NONMEM (version 7) software. Model evaluation was performed using bootstrap analysis, prediction-corrected visual predictive check (pcVPC), as well as standardized visual predictive check (SVPC). The four investigated dose levels showed no difference in log-transformed dose-normalized trough levels of CAS (analysis of variance). CAS concentration data fitted best to a two-compartment model with a proportional-error model, interindividual variability (IIV) fitted best on clearance (CL), central and peripheral volume of distribution (V(1) and V(2), respectively) covariance fitted best on CL and V(1), interoccasion variability (IOV) fitted best on CL, and body weight fitted best as a covariate on CL and V(1) (CL, 0.411 liters/h ± 29% IIV; IOV on CL, 16%; V(1), 5.785 liters ± 29% IIV; intercompartmental clearance, 0.843 liters/h; V2, 6.53 liters ± 67% IIV). None of the other examined covariates (dose level, gender, age, serum bilirubin concentration, creatinine clearance) improved the model further. Bootstrap results showed the robustness of the final PopPK model. pcVPC and SVPC showed the predictability of the model and further confirmed the linear PKs of CAS over the dosage range of 70 to 200 mg QD. On the basis of the final model, geometric mean simulated peak plasma levels at steady state ranged from 13.8 to 39.4 mg/liter (geometric coefficient of variation, 31%), geometric mean trough levels ranged from 4.2 to 12.0 mg/liter (49%), and geometric mean areas under the concentration-time curves ranged from 170 to 487 mg · h/liter (34%) for the dosage range of 70 to 200 mg QD. CAS showed linear PKs across the investigated dosage range of 70 to 200 mg QD. Drug exposure in the present study population was comparable to that in other populations. (This study has been registered with the European Union Drug Regulating Authorities Clinical Trials website under registration no. 2006-001936-30 and at ClinicalTrials.gov under registration no. NCT00404092.).

Population Pharmacokinetics of Methotrexate in Egyptian Children with Lymphoblastic Leukemia

Background: Individualization of high dose regimen of methotrexate (MTX) in pediatric patients with acute lymphoblastic leukemia based on pharmacokinetic (PK) parameters can help in optimization of the dose and better control of the disease. Building up of a pharmacokinetic model can help dose optimization. Objectives: A NONMEM based population (POP) PK model has been subsequently developed to evaluate the effect of demographics as covariates to address variability in pharmacokinetics of MTX. Method: Forty one patients (24 males & 17 females) with ranges of age, body weight and height of 3 - 15 years, 13 - 54 kg and 100 - 177 cm respectively and diagnosed as acute lymphoblastic leukemia (ALL) were involved in the study. MTX was administered as i.v. infusion at a dose of 2 gm/m2 over a period of two hour and its plasma concentrations were determined primarily at 24 hr post-dose to be utilized in the building-up of PK model.The initial/prior estimates of volumes of central (V1) and peripheral compartments (V2) and clearance (CL) and inter-compartmental clearance (Q2) for MTX were extracted from literature. The inter-subject variability was estimated for V1 & CL. The influence of different covariates on model performance and parameter estimates was assessed by evaluating the difference in objective function value. The final POP PK model was validated by bootstrap re-sampling procedures (1000 runs) and the 95% confidence intervals for the estimates were calculated. Results: The POP estimates for CL, V1 and V2 were 2.18 L/h, 5.74 L and 11.2 L respectively. The inter-individual variability for the CL and V1 was 23% and 30% respectively. The covariates analysis showed effect of body surface area and sex on the CL and weight on V1. Conclusions: The POP-PK model developed adequately defines the population PK of MTX in pediatric patients with lymphoblastic leukemia. The model showed effect of body surface area and sex on clearance and weight on volume of distribution of the MTX. Further studies are required on larger number of patients with enrichment of samples for MTX concentrations. The developed PK model should be also investigated in correlation with the genotyping style of different MTX transporters that may affect MTX PK parameters.

Population pharmacokinetics and pharmacogenetics of alcohol in Chinese and Indians in Singapore

Interindividual variability in alcohol pharmacokinetics is influenced by a number of factors, including polymorphisms in genes mediating alcohol pharmacology, ethnicity, sex and body size. Several studies have evaluated the population pharmacokinetics of alcohol from breath alcohol measures. None of these studies, however, have evaluated ethnicity and alcohol-metabolizing enzyme genotypes as covariates in their population pharmacokinetic modelling. We aimed to develop a population pharmacokinetic model using clinical and genetic factors and to identify covariates that influenced interindividual variability in alcohol clearance and volume of distribution. Hundred and eighty healthy subjects (90 Chinese and 90 Indians; 45 males and 45 females from each ethnic group) ingested a vodka-orange juice mixture to simulate social drinking. Subjects were genotyped for the ADH1B (Arg48His), ALDH2 (Glu504Lys) and CYP2E1 (c.-1293G>C and c.-1053C>T) polymorphisms. A base pharmacokinetic model was developed using the nonmem software (NONMEM Project Group, University of California, San Francisco, San Francisco, CA, USA) to determine the alcohol clearance and volume of distribution. The model was extended to include covariates that influenced the between-subject variability. Body weight and sex significantly influenced absorption rate and volume of distribution of alcohol. Body weight and ADH1B Arg48His polymorphism significantly influenced alcohol clearance. The Michaelis-Menten elimination rate (Vmax ) was decreased by 10% in homozygous ADH1B*1/*1 subjects. Ethnicity was not determined to be a significant covariate in the final population pharmacokinetic model. Gender and body weight were covariates that contributed most to explaining the observed interindividual alcohol pharmacokinetic variability. Of the four SNPs examined in this study, only ADH1B Arg48His polymorphism had a significant, though modest, effect on the pharmacokinetics of alcohol.

Population pharmacokinetics of rifampicin in Mexican patients with tuberculosis

Rifampicin (RIF) shows wide variability in its pharmacokinetics. The purpose of this study was to develop and validate a population pharmacokinetic model to characterize the inter- and intra-individual variability in pharmacokinetic parameters of RIF in Mexican patients. Ninety-four patients receiving antituberculosis therapy participated in this prospective study. Plasma concentration-time data were described using a one-compartment model with lag time, absorption and first-order elimination. The potential influence of demographic and clinical characteristics of the patients, and the pharmaceutical formulation (A, B, C and D) on the pharmacokinetics parameters, was evaluated by non-linear mixed-effect modelling (nonmem). Seventy-seven additional patients participated in the validation of the model. The final population pharmacokinetic model obtained was as follows: apparent clearance CL/F = 8·17 L/h (1·40 as high for males), apparent distribution volume V(d)/F = 50·1 L (1·29 as high for males), absorption rate constant K(aA) = 0·391/h, K(aB,C,D) = 2·70/h, relative bioavailability F(A) = 0·468, F(B,C,D) = 1, lag time in the absorption phase T(lag) = 0·264 h. The final model improved the precision on the parameter estimates (CL/F, V(d) /F and K(a) by 31·9%, 16·7% and 92·9%, respectively). The residual variability was 27·3%. Gender was associated with changes in CL/F and V(d) /F whereas the pharmaceutical formulation was associated with changes in F and altered the K(a) . The validation data set showed that the model could be used in clinical practice for Bayesian dose adjustment of RIF in TB patients.

Population pharmacokinetics of lamotrigine in Chinese children with epilepsy

To establish a population pharmacokinetics (PPK) model for lamotrigine (LTG) in Chinese children with epilepsy in order to formulate an individualized dosage guideline. LTG steady-state plasma concentration data from therapeutic drug monitoring (TDM) were collected retrospectively from 284 patients, with a total of 404 plasma drug concentrations. LTG concentrations were determined using a HPLC method. The patients were divided into 2 groups: PPK model group (n=116) and PPK valid group (n=168). A PPK model of LTG was established with NONMEM based on the data from PPK model group according to a one-compartment model with first order absorption and elimination. To validate the basic and final model, the plasma drug concentrations of the patients in PPK model group and PPK valid group were predicted by the two models. The final regression model for LTG was as follows: CL (L/h)=1.01*(TBW/27.87)(0.635)*e(-0.753*VPA)*e(0.868*CBZ)*e(0.633*PB), Vd (L)= 16.7*(TBW/27.87). The final PPK model was demonstrated to be stable and effective in the prediction of serum LTG concentrations by an internal and external approach validation. A PPK model of LTG in Chinese children with epilepsy was successfully established with NONMEM. LTG concentrations can be predicted accurately by this model. The model may be very useful for establishing initial LTG dosage guidelines.

Population pharmacokinetics and pharmacodynamics of bivalirudin in young healthy Chinese volunteers

To investigate the population pharmacokinetics (PK) and pharmacodynamics (PD) of bivalirudin, a synthetic bivalent direct thrombin inhibitor, in young healthy Chinese subjects. Thirty-six young healthy volunteers were randomly assigned into 4 groups received bivalirudin 0.5 mg/kg, 0.75 mg/kg, and 1.05 mg/kg intravenous bolus, 0.75 mg/kg intravenous bolus followed by 1.75 mg/kg intravenous infusion per hour for 4 h. Blood samples were collected to measure bivalirudin plasma concentration and activated clotting time (ACT). Population PK-PD analysis was performed using the nonlinear mixed-effects model software NONMEM. The final models were validated with bootstrap and prediction-corrected visual predictive check (pcVPC) approaches. The final PK model was a two-compartment model without covariates. The typical PK population values of clearance (CL), apparent distribution volume of the central-compartment (V(1)), inter-compartmental clearance (Q) and apparent distribution volume of the peripheral compartment (V(2)) were 0.323 L·h(-1)·kg(-1), 0.086 L/kg, 0.0957 L·h(-1)·kg(-1), and 0.0554 L/kg, respectively. The inter-individual variabilities of these parameters were 14.8%, 24.2%, fixed to 0% and 15.6%, respectively. The final PK-PD model was a sigmoid E(max) model without the Hill coefficient. In this model, a covariate, red blood cell count (RBC(*)), had a significant effect on the EC(50) value. The typical PD population values of maximum effect (E(max)), EC(50), baseline ACT value (E(0)) and the coefficient of RBC(*) on EC(50) were 318 s, 2.44 mg/L, 134 s and 1.70, respectively. The inter-individual variabilities of E(max), EC(50), and E(0) were 6.80%, 46.4%, and 4.10%, respectively. Population PK-PD models of bivalirudin in healthy young Chinese subjects have been developed, which may provide a reference for future use of bivalirudin in China.

Development of population PK model with enterohepatic circulation for mycophenolic acid in patients with childhood‐onset systemic lupus erythematosus

This study aimed to develop a population pharmacokinetic (PK) enterohepatic recycling model for MPA in patients with childhood-onset systemic lupus erythematosus (cSLE). MPA concentration-time data were from outpatients on stable oral mycophenolate mofetil (MMF) and collected under fasting conditions, with standardized meals (1 and 4 h post-dose). Sampling times were pre-dose, 20, 40 min, 1, 1.5, 2, 3, 4, 6 and 9 h, post dose. The population PK analysis simultaneously modelled MPA and 7-O-MPA-β-glucuronide (MPAG) concentrations using nonlinear mixed effect modelling. PK analysis included 186 MPA and MPAG concentrations (mg l(-1)) from 19 patients. cSLE patients, age range 10-28 years, median 16.5 years were included. Mean ± SD disease duration was 3.8 ± 3.7 years. The final PK model included a gallbladder compartment for enterohepatic recycling and bile release time related to meal times, with first order absorption and single series of transit compartments. The PK estimates for MPA were CL(1) /F 25.3 l h(-1), V(3) /F 20.9 l, V(4) /F 234 l and CL(2) /F 19.8 l h(-1). The final model fitted the complex processes of absorption and enterohepatic circulation (EHC) in those treated with MMF for cSLE and could be applied in Bayesian dose optimization algorithms.

Population Pharmacokinetics of Metronidazole Evaluated Using Scavenged Samples from Preterm Infants

Pharmacokinetic (PK) studies in preterm infants are rarely conducted due to the research challenges posed by this population. To overcome these challenges, minimal-risk methods such as scavenged sampling can be used to evaluate the PK of commonly used drugs in this population. We evaluated the population PK of metronidazole using targeted sparse sampling and scavenged samples from infants that were ≤ 32 weeks of gestational age at birth and <120 postnatal days. A 5-center study was performed. A population PK model using nonlinear mixed-effect modeling (NONMEM) was developed. Covariate effects were evaluated based on estimated precision and clinical significance. Using the individual Bayesian PK estimates from the final population PK model and the dosing regimen used for each subject, the proportion of subjects achieving the therapeutic target of trough concentrations >8 mg/liter was calculated. Monte Carlo simulations were performed to evaluate the adequacy of different dosing recommendations per gestational age group. Thirty-two preterm infants were enrolled: the median (range) gestational age at birth was 27 (22 to 32) weeks, postnatal age was 41 (0 to 97) days, postmenstrual age (PMA) was 32 (24 to 43) weeks, and weight was 1,495 (678 to 3,850) g. The final PK data set contained 116 samples; 104/116 (90%) were scavenged from discarded clinical specimens. Metronidazole population PK was best described by a 1-compartment model. The population mean clearance (CL; liter/h) was determined as 0.0397 × (weight/1.5) × (PMA/32)²·⁴⁹ using a volume of distribution (V) (liter) of 1.07 × (weight/1.5). The relative standard errors around parameter estimates ranged between 11% and 30%. On average, metronidazole concentrations in scavenged samples were 30% lower than those measured in scheduled blood draws. The majority of infants (>70%) met predefined pharmacodynamic efficacy targets. A new, simplified, postmenstrual-age-based dosing regimen is recommended for this population. Minimal-risk methods such as scavenged PK sampling provided meaningful information related to development of metronidazole PK models and dosing recommendations.