The purpose of these studies was to establish human-simulated regimens of cefepime and taniborbactam in the murine pneumonia model equivalent to clinical doses of 2 and 0.5 g, respectively, administered every 8 h as 4 h infusions based on the unbound (free) plasma exposures. Following the selection and the confirmation of the cefepime and taniborbactam human-simulated regimens, additional studies were conducted to quantify the plasma and bronchopulmonary exposures achieved following the administration of the taniborbactam dosages utilized in the dose-ranging studies in combination with the cefepime human-simulated regimen.
Cefepime pharmacokinetic data in healthy adult volunteers collected in Phase I studies upon taniborbactam co-administration8 (link) and cefepime and taniborbactam pharmacokinetic parameters in the murine model were utilized for simulation. Cefepime protein-binding percentages utilized in the simulations were 20% and 0% in humans and mice, respectively,9 (link) while taniborbactam protein-binding percentages were 0% and 19.4% in humans10 and mice,11 (link) respectively.
Infected mice (6–10 groups of six mice each) received the estimated human-simulated regimen of cefepime as monotherapy or in combination with that of taniborbactam or fractions of the established taniborbactam human-simulated regimen: 1.56% or 12.5% of the taniborbactam human-simulated regimen doses (equivalent to 7.8 or 62.5 mg every 8 h as 4 h infusion, respectively).
At 6–10 different timepoints, groups of six mice were euthanized by CO2 asphyxiation followed by blood collection via intracardiac puncture and cervical dislocation. Following blood collection, but prior to cervical dislocation, bronchoalveolar lavage (BAL) fluid was collected from the mice at the same timepoints using methods previously described.12 Formic acid in water (2% v/v) was added to BAL samples (equal parts) prior to freezing. All sample tubes were stored at −80°C until drug and urea concentration determination. Cefepime, taniborbactam and urea concentrations in plasma and BAL fluid were assayed by either Keystone Bioanalytical, Inc. (North Wales, PA, USA) or by Venatorx Pharmaceuticals, Inc. using qualified LC-MS/MS methods.
Cefepime and taniborbactam concentrations in the epithelial lining fluid (ELF) were estimated by correcting the drug concentration in BAL fluid for the dilution with NS during lavage using the following formula13 (link):
CompoundELF = CompoundBAL × (Ureaplasma/UreaBAL), where CompoundBAL is the measured concentration of either cefepime or taniborbactam in the BAL fluid sample and Ureaplasma and UreaBAL are the concentrations of urea in paired plasma and BAL fluid samples from each mouse, respectively.
Statistical outliers for each respective analyte were removed by the IQR method. A pharmacokinetic model was fitted to the plasma and ELF concentrations of each of cefepime and taniborbactam and the best-fit estimate parameters were determined by the non-linear least-squares techniques (WinNonlin, Version 8.3, Pharsight Corp., Mountain View, CA, USA). Compartment model selection was based on visual inspection of the fit and comparison of model diagnostics.
These parameters were utilized to estimate the plasma and ELF exposures and the ELF penetration ratios as the ratio of the ELF AUC0–24 to unbound (free) plasma AUC0–24.
Cefepime pharmacokinetic data in healthy adult volunteers collected in Phase I studies upon taniborbactam co-administration8 (link) and cefepime and taniborbactam pharmacokinetic parameters in the murine model were utilized for simulation. Cefepime protein-binding percentages utilized in the simulations were 20% and 0% in humans and mice, respectively,9 (link) while taniborbactam protein-binding percentages were 0% and 19.4% in humans10 and mice,11 (link) respectively.
Infected mice (6–10 groups of six mice each) received the estimated human-simulated regimen of cefepime as monotherapy or in combination with that of taniborbactam or fractions of the established taniborbactam human-simulated regimen: 1.56% or 12.5% of the taniborbactam human-simulated regimen doses (equivalent to 7.8 or 62.5 mg every 8 h as 4 h infusion, respectively).
At 6–10 different timepoints, groups of six mice were euthanized by CO2 asphyxiation followed by blood collection via intracardiac puncture and cervical dislocation. Following blood collection, but prior to cervical dislocation, bronchoalveolar lavage (BAL) fluid was collected from the mice at the same timepoints using methods previously described.12 Formic acid in water (2% v/v) was added to BAL samples (equal parts) prior to freezing. All sample tubes were stored at −80°C until drug and urea concentration determination. Cefepime, taniborbactam and urea concentrations in plasma and BAL fluid were assayed by either Keystone Bioanalytical, Inc. (North Wales, PA, USA) or by Venatorx Pharmaceuticals, Inc. using qualified LC-MS/MS methods.
Cefepime and taniborbactam concentrations in the epithelial lining fluid (ELF) were estimated by correcting the drug concentration in BAL fluid for the dilution with NS during lavage using the following formula13 (link):
CompoundELF = CompoundBAL × (Ureaplasma/UreaBAL), where CompoundBAL is the measured concentration of either cefepime or taniborbactam in the BAL fluid sample and Ureaplasma and UreaBAL are the concentrations of urea in paired plasma and BAL fluid samples from each mouse, respectively.
Statistical outliers for each respective analyte were removed by the IQR method. A pharmacokinetic model was fitted to the plasma and ELF concentrations of each of cefepime and taniborbactam and the best-fit estimate parameters were determined by the non-linear least-squares techniques (WinNonlin, Version 8.3, Pharsight Corp., Mountain View, CA, USA). Compartment model selection was based on visual inspection of the fit and comparison of model diagnostics.
These parameters were utilized to estimate the plasma and ELF exposures and the ELF penetration ratios as the ratio of the ELF AUC0–24 to unbound (free) plasma AUC0–24.
