Pharmacokinetic and Pharmacodynamic Target Attainment in Adult and Pediatric Patients Following Administration of Ceftaroline Fosamil as a 5-Minute Infusion.

The key pharmacokinetic/pharmacodynamic (PK/PD) efficacy index for ß-lactam antibiotics is the percentage of time that free drug concentrations exceed the minimum inhibitory concentration (MIC) of bacteria during each dosing interval (fT>MIC). Ceftaroline fosamil, the prodrug of the ß-lactam ceftaroline, was initially approved for administration as 60-minute intravenous (IV) infusions. Population PK analyses comparing exposure and PK/PD target attainment for 5-minute and 60-minute IV infusions, described here, have supported ceftaroline fosamil labeling updates to include variable infusion durations of 5 to 60 minutes in adults and children aged ≥2 months. A 2-compartment disposition PK model for ceftaroline fosamil and ceftaroline was used to predict steady-state ceftaroline exposures (maximum plasma concentrations [Cmax,ss ] and area under the plasma concentration-time curve over 24 hours [AUCss,0-24 ]) and probability of target attainment in simulated adult and pediatric patients with various degrees of renal function receiving standard doses of ceftaroline fosamil as 5-minute or 60-minute IV infusions. Across age groups and renal function categories, median ceftaroline AUCss,0-24 values were similar for 5-minute and 60-minute infusions, whereas Cmax,ss was up to 42% higher for 5-minute infusions. Both infusion durations achieved >99% probability of target attainment based on PK/PD targets for Staphylococcus aureus (35% fT>MIC) and Streptococcus pneumoniae (44% fT>MIC) at European Committee on Antimicrobial Susceptibility Testing/Clinical and Laboratory Standards Institute MIC breakpoints (1 mg/L and 0.25/0.5 mg/L, respectively). These findings support administration of standard ceftaroline fosamil doses over 5 to 60 minutes for adults and children aged ≥2 months, providing added flexibility to clinicians and patients.

Population Pharmacokinetic Analysis of Pexidartinib in Healthy Subjects and Patients With Tenosynovial Giant Cell Tumor or Other Solid Tumors.

Pexidartinib is a kinase inhibitor that induces tumor response and improvements in symptoms and functional outcomes in adult patients with symptomatic tenosynovial giant cell tumor (TGCT). A population pharmacokinetic (PK) model for pexidartinib and its metabolite, ZAAD, was developed, and effects of demographic and clinical factors on the PK of pexidartinib and ZAAD were estimated. The analysis included pooled data from 7 studies in healthy volunteers (N = 159) and 2 studies in patients with TGCT or other solid tumors (N = 216). A structural 2-compartment model with sequential zero- and first-order absorption and lag time, and linear elimination from the central compartment adequately described pexidartinib and ZAAD PKs. Clearance of pexidartinib was estimated at 5.83 L/h in a typical patient with reference covariates (male, non-Asian, weight = 80 kg, creatinine clearance ≥90 mL/min, aspartate aminotransferase ≤80 U/L, and total bilirubin ≤20.5 µmol/L). In the covariate analysis, Asians and healthy subjects had modestly lower pexidartinib exposure (21% decrease each) in terms of steady-state area under the curve values from 0 to 24 hours (AUC0-24,ss ). Effects of body weight, sex, and hepatic function parameters on pexidartinib AUC0-24,ss were generally <20%. Patients with TGCT with mild renal impairment were predicted to have approximately 23% higher AUC0-24,ss than those with normal renal function. The effects of covariates on ZAAD exposure were similar to those on pexidartinib. These results indicate small and generally clinically nonmeaningful effects of patient demographic and clinical characteristics on pexidartinib and ZAAD PK profiles.

Population pharmacokinetics of adalimumab biosimilar adalimumab-adbm and reference product in healthy subjects and patients with rheumatoid arthritis to assess pharmacokinetic similarity.

AIMS: Adalimumab-adbm is a monoclonal antibody developed as a biosimilar to adalimumab (Humira, AbbVie Inc.). The key objectives of this study were using a population pharmacokinetic (PPK) approach to assess pharmacokinetic (PK) similarity between adalimumab-adbm and Humira in patients with active rheumatoid arthritis (RA), to quantify the effects of potential covariates on adalimumab PK and to assess the impact of switching treatment from Humira to adalimumab-adbm on PK. METHODS: A PPK model was firstly developed using intensive PK data from the phase-1 study in healthy subjects (NCT02045979). PPK models were developed separately for phase-3 base study (NCT02137226) and its extension study (NCT02640612) in patients with active RA. RESULTS: PPK models were developed for adalimumab from adalimumab-adbm and Humira treatment in healthy subjects and RA patients. Weight and anti-drug antibodies were found to be important predictors of adalimumab clearance. Adalimumab PK was similar between adalimumab-adbm and Humira. The estimated effect of Humira on clearance, relative to the adalimumab-adbm, was 1.02 (i.e., Humira has 0.02 greater clearance). Similarly, the effect of treatment arms (switching) on clearance was estimated to be 1.00 and 0.997 for Humira:Humira:BI and Humira:BI:BI arms, respectively, relative to the BI:BI:BI arm (BI refers to adalimumab-adbm) in the phase-3 extension study. CONCLUSION: PK similarity between adalimumab-adbm and Humira in patients with active RA was demonstrated using PPK approach. Adalimumab PK was also similar when switching treatment from Humira to adalimumab-adbm at either week 24 or 48.

Population PK Modeling and Target Attainment Simulations to Support Dosing of Ceftaroline Fosamil in Pediatric Patients With Acute Bacterial Skin and Skin Structure Infections and Community-Acquired Bacterial Pneumonia.

Ceftaroline, the active form of the prodrug ceftaroline fosamil, is approved for use in adults with community-acquired bacterial pneumonia (CABP) or acute bacterial skin and skin structure infections (ABSSSI) in the United States and for similar indications in Europe. Pharmacokinetic (PK) data from 5 pediatric (birth to <18 years) studies of ceftaroline fosamil were combined with PK data from adults to update a population PK model for ceftaroline and ceftaroline fosamil. This model, based on a data set including 305 children, was used to conduct simulations to estimate ceftaroline exposures and percentage of time that free drug concentrations were above the minimum inhibitory concentration (%fT>MIC) for pediatric dose regimens. With dose regimens of 8 mg/kg every 8 hours (q8h) in children aged 2 months to <2 years and 12 mg/kg (up to a maximum of 400 mg) q8h in children aged 2 years to <18 years or 600 mg q12h in children aged 12 to <18 years, >90% of children were predicted to achieve a target of 36% fT>MIC at an MIC of 2 mg/L, and >97% were predicted to achieve 44% fT>MIC at an MIC of 1 mg/L. Thus, high PK/pharmacodynamic target attainment would be maintained in children for targets associated with 1-log kill of Staphylococcus aureus and Streptococcus pneumoniae. The predicted ceftaroline exposures for these dose regimens were similar to those in adults given 600 mg q12h ceftaroline fosamil. This work contributed to the approval of dose regimens for children aged 2 months to <18 years by the FDA and EMA, which are presented.

Penetration of Ceftaroline into the Epithelial Lining Fluid of Healthy Adult Subjects.

Ceftaroline, the active metabolite of the prodrug ceftaroline fosamil, is a cephalosporin with bactericidal activity against Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA). This study aimed to (i) evaluate ceftaroline concentrations in human plasma and epithelial lining fluid (ELF) and (ii) develop a population pharmacokinetic (PK) model for plasma and ELF to be used in PK/pharmacodynamic (PD) target attainment simulations. Ceftaroline concentrations in ELF and plasma at steady state (day 4) were measured in healthy adult subjects for two dosages: 600 mg every 12 h (q12h) and 600 mg every 8 h (q8h). Both were well tolerated with no serious adverse events. The penetration of free ceftaroline into ELF, assuming 20% protein binding in plasma and no protein binding in ELF, was ≈23%. The population PK model utilized a two-compartment model for both ceftaroline fosamil and ceftaroline. Goodness-of-fit criteria revealed the model was consistent with observed data and no systematic bias remained. At 600 mg q12h and a MIC of 1 mg/liter, 98.1% of simulated patients would be expected to achieve a target free drug concentration above the MIC (fT>MIC) in plasma of 42%, and in ELF 81.7% would be expected to achieve a target fT>MIC of 17%; at 600 mg q8h, 100% were predicted to achieve an fT>MIC in plasma of 42% and 94.7% to achieve an fT>MIC of 17% in ELF. The literature and data suggest the 600 mg q12h dose is adequate for MICs of ≤1 mg/liter. There is a need for clinical data in patients with MRSA pneumonia and data to correlate PK/PD relationships in ELF with clinical outcomes.

Population Pharmacokinetic Modeling of Guanfacine in Pediatric Patients.

INTRODUCTION: The population pharmacokinetics of guanfacine extended release were characterized in pediatric patients aged 6-17 years using NONMEM and evaluated by predictive check and bootstrap. METHODS: Data were described using a one-compartment model. A covariate modeling approach that emphasized parameter estimation rather than stepwise hypothesis testing was implemented. A nonparametric bootstrap procedure and a predictive check method were used to evaluate the final model and parameter estimates. RESULTS: Typical population pharmacokinetic parameters (95 % confidence interval), given the reference covariates (Caucasian, male, age 12 years, weight 50 kg), were 33.1 (30.2-36.4) L/h for apparent clearance (CL/F), 804 (703-900) L for apparent volume of distribution, 0.552 (0.437-0.670) h(-1) for the absorption rate constant, and 0.651 (0.608-0.697) h for absorption lag time. DISCUSSION: The pharmacokinetics of guanfacine are similar in pediatric patients compared with adults when appropriately scaled by patient weight. The main predictor of guanfacine exposure, as determined by a change in CL/F, was weight. Effects of the other covariates (age, sex, and race) on CL/F were estimated with reasonable precision; however, the additional effects of age, sex, and race can be considered to have little to no clinical relevance.

Modeling and simulation of the exposure-response and dropout pattern of guanfacine extended-release in pediatric patients with ADHD.

Guanfacine extended-release (GXR) is a selective α2A-adrenergic receptor agonist approved in the United States for once-daily administration for the treatment of attention-deficit hyperactivity disorder (ADHD) in children and adolescents ages 6-17 years old either as monotherapy or adjunctive to stimulant medications. This analysis integrates exposure-response, placebo, and dropout data from 10 clinical trials that used GXR in adolescents and children with ADHD. In these trials, the ADHD Rating Scale-IV (ADHD RS-IV) score was collected longitudinally within patients over the course of 6-13 weeks. Non-linear mixed effects models were developed and used to describe the exposure-response of the GXR and placebo time course. The OpenBUGS program was utilized to describe the dropout time course across the trials. Placebo time course was best described by an inverse Bateman function with a 3-group mixture model that allowed for the onset and offset of the placebo response. Dropout time modeling indicated a missing at random mechanism for dropouts which was best described by a Weibull distribution with an estimated percentage of non-dropout patients. A linear exposure-response model with an adolescent effect on maximum slope (SLPmax), and a time delay for reaching SLPmax, provided the best description of the GXR exposure-response time course. The GXR exposure-response model indicated that the typical (95 % confidence interval) decrease in ADHD RS-IV score from the placebo-response trajectory would be 37.1 % (32.2, 42.0 %) per 0.1 mg/kg of GXR exposure. There was little noticeable difference between the exposure-response in adolescents and children or across ADHD subtypes.

Population pharmacokinetic/pharmacodynamic modeling of guanfacine effects on QTc and heart rate in pediatric patients.

Using a previously developed population pharmacokinetic model, an exposure-response (ER) model was successfully developed to describe guanfacine plasma concentrations and changes in heart rate (HR) and the QT interval. Guanfacine exposure was associated with small decreases in HR and a small prolongation of the population-corrected QT (QTcP) interval. Based on the final ER model for effect of guanfacine on HR, the estimated population typical decrease in HR would be 2.3% (2.1-2.7%) of the baseline circadian HR for every 1 ng/mL of guanfacine exposure. A QTcP was developed for the analysis using the sampled population. An effect of sex on baseline-corrected QT (BQTP) was the only covariate effect in the final ER model for QTcP, its inclusion resulting in a typical baseline QTcP estimate that is 9 (5-13) ms higher for females. There was no evidence of QT-RR hysteresis. A linear model was used to relate guanfacine plasma concentrations to QTcP. The typical (95% confidence interval) slope parameter was estimated to be 0.941 (0.62-1.25) ms/ng/mL. The final model predicted an approximate 1-ms increase from baseline for every 1 ng/mL of guanfacine in plasma. The main predictor of QTcP prolongation was guanfacine exposure, which decreased with body weight and increased with dose.

Population pharmacokinetics of atorvastatin and its active metabolites in children and adolescents with heterozygous familial hypercholesterolemia: selective use of informative prior distributions from adults.

The population pharmacokinetics (PPK) of atorvastatin and its principal active metabolite, o-hydroxyatorvastatin, were described in 6-17 years old pediatric hypercholesterolemia patients with a 2-compartment model for both parent and metabolite. Informative prior distributions on selected parameters, based on adult data, were required to stabilize the model and were implemented using a Bayesian penalty term on the likelihood function in the nonlinear mixed effects model (NONMEM VI with PRIOR). Concentrations below the limit of quantitation were treated as censored data using a conditional likelihood function. Atorvastatin apparent oral clearance (CL/F) was described as a function of body weight using an allometric equation. Based on the final model, the typical CL/F estimates for a Tanner Stage 1 patient (35 kg weight) and Tanner Stage ≥2 (50 kg weight), would be 553 and 543 L/hour, respectively. When scaled allometrically, CL/F was similar to values reported for adults. Variability in atorvastatin PK was primarily affected by weight.

Facilitating pharmacometric workflow with the metrumrg package for R.

metrumrg is an R package that facilitates workflow for the discipline of pharmacometrics. Support is provided for data preparation, modeling, simulation, diagnostics, and reporting. Existing tools and techniques are emphasized where available; original solutions are provided for otherwise unmet needs. In particular, metrumrg implements an R interface for the NONMEM(®) modeling software, optionally run in a distributed computing environment. The paradigm allows start-to-finish analyses in a single scripting language. Emphasis on text-based formats promotes traceability of results.

Population pharmacokinetic-pharmacodynamic analysis of istradefylline in patients with Parkinson disease.

This model-based analysis quantifies the population pharmacokinetic-pharmacodynamic efficacy and safety/tolerability relationships of orally administered istradefylline, a selective adenosine A(2A) receptor antagonist, in healthy participants and patients with Parkinson disease. Data from 6 phase 2/3 clinical trials comprised the population database, with 1760 and 1798 patients contributing to the efficacy and safety/tolerability analyses, respectively. The relationship between istradefylline area under the curve at steady state and percentage OFF time was described by a nonlinear model (Emax) based on time for the disease progression/placebo response component and an Emax model for the effect of istradefylline. The typical maximum decrease in percentage OFF time due to istradefylline exposure would be 5.79% (95% confidence interval = 4.09%-7.49%) with one-half of the maximum effect reached at an exposure of 1690 ng × hr/mL (95% confidence interval = 199-3180 ng × hr/mL). The pharmacokinetic-pharmacodynamic relationships for dyskinesia and dizziness were described by an Emax model, and for nausea, a power model was used. The probabilities of dyskinesia and dizziness are expected to plateau at a dose of 40 mg/d, and the probability of nausea is expected to continually rise as the dose is increased. Collectively, these results support a starting istradefylline dose of 20 to 40 mg/d.

Population pharmacokinetic analysis of istradefylline in healthy subjects and in patients with Parkinson's disease.

This model-based analysis quantifies the population pharmacokinetics (PK) of orally administered istradefylline, a selective adenosine A(2A) receptor antagonist, in healthy subjects and patients with Parkinson's disease, including the estimation of covariate effects on istradefylline PK parameters. Istradefylline plasma concentration data from 8 phase 1 and 8 phase 2/3 studies conducted in 1449 patients and normal, healthy volunteers aged from 18 to 87 years were best described by a 2-compartment model with first-order absorption parameterized in terms of apparent oral clearance (CL/F), apparent central volume of distribution (V2/F), apparent intercompartmental clearance (Q/F), apparent peripheral volume of distribution (V3/F) and a first-order absorption rate-constant (Ka). The typical population PK parameters were CL/F (5.76 L/h), V2/F (198 L), Q (21.6 L/h), V3/F (307 L), and Ka (0.464 h(-1)) for a 70-kg, nonsmoking Caucasian who had 55.6 kg of lean body mass, no presence of CYP3A4 inhibitors, and unknown food status. Smoking and CYP3A4 inhibitors as concomitant medications were important predictors of istradefylline exposure. Istradefylline area under the concentration-time curve at steady-state increased 35% (95% confidence interval, 18%-55%) in the presence of CYP3A4 inhibitors and decreased 38% (95% confidence interval, 26%-50%) in smokers. The population PK model described the observed concentration data well and was deemed appropriate for further evaluation of the istradefylline exposure-response relationship in patients with Parkinson's disease.

Population pharmacokinetic modeling of epoetin delta in pediatric patients with chronic kidney disease.

This analysis quantifies the population pharmacokinetics of subcutaneous and intravenous epoetin delta, an epoetin produced in a human cell line, in pediatric patients with chronic kidney disease and estimates the effects of covariate factors on epoetin delta and epoetin alfa pharmacokinetic parameters. Erythropoietin serum concentration data, taken from a phase III study conducted in 60 patients aged 1 to 17 years, were best described by a 1-compartment model with first-order absorption and elimination. The typical point estimates were clearance (0.268 L/h), central volume of distribution (1.03 L), absorption rate constant (0.0554 h(-1)), and bioavailability (0.708) for a 35-kg male < or = 10 years who was predialysis and on subcutaneous epoetin delta treatment. Erythropoietin pharmacokinetic parameters were similar in pediatric patients as compared with adults when scaled by weight. The subcutaneous administration of epoetin alfa exhibited lower systemic bioavailability than subcutaneous administration of epoetin delta.

Population pharmacokinetics of daptomycin.

Data from subjects in nine phase 1 (n = 153) and six phase 2/3 (n = 129) clinical trials were combined to identify factors contributing to interindividual variability in daptomycin pharmacokinetics (PK). Over 30 covariates were considered. A two-compartment model with first-order elimination provided the best fit for data on daptomycin concentrations in plasma over time. In the final population PK model, daptomycin plasma clearance (CL) was a function of renal function, body temperature, and sex. Of these factors, renal function contributed most significantly to interindividual variability. CL varied linearly with the estimated creatinine clearance. CL among dialysis subjects was approximately one-third that of healthy subjects (0.27 versus 0.81 liter/h). CL in females was 80% that in males; however, in clinical trials, the outcome was not affected by sex and therefore this effect is not considered clinically meaningful. The relationship with body temperature should be interpreted cautiously since the analysis included only a limited number of subjects who were hyperthermic. The volume of distribution of the peripheral compartment (V2) and intercompartmental clearance (Q) were linearly related to body weight. V2 increased approximately twofold in the presence of an acute infection. No factors were identified that significantly impacted V1. This analysis supports the dosing of daptomycin on a milligram-per-kilogram-of-body-weight basis and suggests that modified dosing regimens are indicated for patients with severe renal disease and for those undergoing dialysis.

Population pharmacokinetic analysis of anidulafungin, an echinocandin antifungal.

The objective of this analysis was to describe the pharmacokinetic characteristics of anidulafungin in patients with serious fungal disease based on pharmacokinetic data collected during four recently completed or ongoing Phase II/III clinical studies. A total of 600 anidulafungin plasma samples from 225 patients across the four studies were available for analysis. Patients received daily intravenous infusions of 50, 75, or 100 mg anidulafungin, preceded by a loading dose that was twice the daily dose. The analysis population consisted of 129 patients with esophageal candidiasis, 87 with invasive candidiasis, 7 with invasive aspergillosis, and 2 with azole refractory mucosal candidiasis. A population analysis approach was used to develop a steady-state pharmacokinetic model for anidulafungin, assess the significance of possible covariates, and determine the amount of intersubject and random residual variability. A two-compartment model with first-order elimination provided the best fit to the data. The clearance of anidulafungin was influenced by weight and gender, and subjects in the invasive candidiasis study had a typical clearance that was approximately 30% higher than subjects from other studies. Weight was determined to be a predictor of the central volume of distribution. The covariates on clearance accounted for less than 20% of the intersubject variability and therefore are deemed to be of little clinical relevance. There was no evidence that the presence of rifampin or metabolic substrates, inhibitors, or inducers of cytochrome p450 influenced the clearance of anidulafungin. This indicates that dosing adjustments are not necessary when anidulafungin is administered in the presence of medications falling into these classifications.