Development of breakpoints of carbapenems for intraabdominal infections based on pharmacokinetics and pharmacodynamics in peritoneal fluid

This study aimed to develop breakpoints of carbapenems for intraabdominal infections, based on pharmacokinetics (PK) and pharmacodynamics (PD) at the target site. Imipenem, meropenem, and doripenem were each administered to 8–11 patients before abdominal surgery, and venous blood and peritoneal fluid samples were obtained. The drug concentrations in plasma and peritoneal fluid were determined and analyzed using population pharmacokinetic modeling. Using the pharmacokinetic model parameters, a Monte Carlo simulation was performed to estimate the probabilities of attaining the bacteriostatic and bactericidal targets (20% and 40% of the time above the minimum inhibitory concentration [MIC], respectively) in peritoneal fluid. The bacteriostatic and bactericidal breakpoints were defined as the highest MIC values at which the bacteriostatic and bactericidal probabilities in peritoneal fluid were 80% or more. The breakpoints for the minimum and maximum approved dosages of each drug were identical for imipenem, meropenem, and doripenem, and some of these values varied with dosing interval and infusion time. Site-specific PK-PD-based breakpoints are proposed here for the first time, and should help us to select appropriate carbapenem regimens for intraabdominal infections.