Population Pharmacokinetic Analyses for Ertapenem in Subjects with a Wide Range of Body Sizes

The Importance of Assessing Drug Pharmacokinetics and Pharmacodynamics in the Obese Population During Drug Development

Obesity remains a US national health crisis and a growing concern worldwide. Concerningly, individuals who are obese are at an increased risk for comorbid diseases that include, but are not limited to, hypertension, diabetes, cardiovascular disease, and cancer. Beyond the risk for developing these conditions, obesity may also impact the pharmacological activity of the therapies being used to treat them and other disease states. The pharmacokinetics (PK), pharmacodynamics (PD), safety, and efficacy of therapies, both currently marketed and under clinical development, may be directly impacted by the physiological alterations that occur secondary to the occurrence of chronic excess body weight. The increased prevalence of this disease should not be ignored. Both private and federal institutions involved in drug research and development should consider, as appropriate, a greater inclusion of individuals who are obese in clinical trials throughout the entirety of drug development, and leverage the available PK, PD, safety, and efficacy data to make more informed dosing recommendations.

Drug pharmacokinetics in the obese population: challenging common assumptions on predictors of obesity-related parameter changes

INTRODUCTION

Obesity is associated with many physiological changes. We review available evidence regarding five commonly accepted assumptions to a priori predict the impact of obesity on drug pharmacokinetics (PK).

AREAS COVERED

The investigated assumptions are: 1) lean body weight is the preferred descriptor of clearance and dose adjustments; 2) volume of distribution increases for lipophilic, but not for hydrophilic drugs; 3) CYP-3A4 activity is suppressed and UGT activity is increased, implying decreased and increased dose requirements for substrates of these enzyme systems, respectively; 4) glomerular filtration rate is enhanced, necessitating higher doses for drugs cleared through glomerular filtration; 5) drug dosing information from obese adults can be extrapolated to obese adolescents.

EXPERT OPINION

Available literature contradicts, or at least limits the generalizability, of all five assumptions. Clinical studies should focus on quantifying the impact of duration and severity of obesity on drug PK in adults and adolescents, and also include oral bioavailability and pharmacodynamics in these studies. Physiologically-based PK approaches can be used to predict PK changes for individual drugs, but can also be used to define in general terms based on patient characteristics and drug properties, when certain assumptions can or cannot be expected to be systematically accurate.

Pharmacokinetics of Ertapenem in Sheep (Ovis aries) with Experimentally Induced Urinary Tract Infection

Sheep are commonly used as animal models for human biomedical research, but descriptions of their use for studying the pharmacokinetics of carbapenem antimicrobials, such as ertapenem, are unavailable. Ertapenem is a critical antimicrobial for human infections, and the description of the pharmacokinetics of this drug is of value for research using ovine as models for human diseases, such as urinary tract infections (UTI). There are currently no ovine models for comparative biomedical research of UTI. The objective of this study was to report the pharmacokinetics of ertapenem in sheep after single and multiple dosing. In addition, we explored the effects of an immunomodulatory drug (Zelnate) on the pharmacokinetics of ertapenem in sheep. Eight healthy ewes (weight, 64.4 ± 7.7 kg) were used in an ovine bacterial cystitis model of human cystitis with Pseudomonas aeruginosa. After disease confirmation, each ewe received 1 g of ertapenem intravenously once every 24 h for 5 administrations. Blood was collected intensively (14 samples) during 24 h after the first and last administration. After multiple-dose administration, the volume of distribution was 84.5 mL/kg, clearance was 116.3 mL/h/kg, T1/2₍λ_z) was 1.1 h, and the extraction ratio was 0.02. No significant differences in pharmacokinetic parameters or time points were found between groups treated with the immunostimulant and controls or after the 1st or 5th administration of ertapenem. No accumulation was noted from previous administration. Our ovine pharmacokinetic findings can be used to evaluate therapeutic strategies for ertapenem use (varying drug dosing schedules and combinations with other antimicrobials or immune modulators) in the context of UTI.

Pharmacokinetic-Pharmacodynamic Evaluation of Ertapenem for Patients with Hospital-Acquired or Ventilator-Associated Bacterial Pneumonia

Ertapenem provides activity against many pathogens commonly associated with hospital-acquired and ventilator-associated bacterial pneumoniae (HABP and VABP, respectively), including methicillin-susceptible Staphylococcus aureus and numerous Gram-negative pathogens with one major gap in coverage, Pseudomonas aeruginosa Pharmacokinetic-pharmacodynamic (PK-PD) target attainment analyses were conducted to evaluate ertapenem against the most prevalent Enterobacteriaceae causing HABP/VABP. The objective of these analyses was to provide dose selection support for and demonstrate the appropriateness of ertapenem to empirically treat patients with HABP/VABP when administered with murepavadin, a novel targeted antimicrobial exhibiting a highly specific spectrum of activity against P. aeruginosa A previously developed population pharmacokinetic model, a total-drug epithelial lining fluid (ELF) to free-drug serum penetration ratio, contemporary in vitro surveillance data for ertapenem against Enterobacteriaceae, and percentage of the dosing interval for which drug concentrations exceed the MIC value (%T>MIC) targets associated with efficacy were used to conduct Monte Carlo simulations for five ertapenem regimens administered over short or prolonged durations of infusion. Overall total-drug ELF percent probabilities of PK-PD target attainment based on a %T>MIC target of 35% among simulated patients with HABP/VABP arising from Enterobacteriaceae based on pathogen prevalence data for nosocomial pneumonia ranged from 89.1 to 92.7% for all five ertapenem regimens evaluated. Total-drug ELF percent probabilities of PK-PD target attainment ranged from 99.8 to 100%, 97.9 to 100%, 10.6 to 74.1%, and 0 to 1.50% at MIC values of 0.06, 0.12, 1, and 4 μg/ml, respectively (MIC₉₀ values for Escherichia coli, Serratia marcescens, Enterobacter species, and Klebsiella pneumoniae, respectively). Results of these analyses provide support for the evaluation of ertapenem in combination with murepavadin for the treatment of patients with HABP/VABP.