Caspofungin Population Pharmacokinetic Analysis in Plasma and Peritoneal Fluid in Septic Patients with Intra-Abdominal Infections: A Prospective Cohort Study.

Objectives: The aim of this study was to report the pharmacokinetics (PK) of caspofungin in plasma and peritoneal fluid and to identify optimal dosing strategies in septic patients with intra-abdominal infections.

Methods: Eleven patients with secondary peritonitis with septic shock received the standard dosing regimen of caspofungin. Total caspofungin plasma and peritoneal concentrations were subject to a population PK analysis using Pmetrics. Monte Carlo simulations were performed considering the ratio of 24-h total drug exposure above the minimum inhibitory concentration (AUC/MIC) in plasma and comparing simulated concentrations versus MIC in peritoneal fluid.

Results: Fat-free mass (FFM) was retained in the final model of caspofungin, reporting a total clearance (standard deviation) of 0.78 (0.17) L/h and a central volume of distribution of 9.36 (2.61) L. The peritoneal fluid/plasma ratio of caspofungin was 33% on the first day of therapy (AUC 73.92 (21.93) and 26.03 (9.88) mg*h/L for plasma and peritoneal data, respectively). Dosing simulations supported the use of standard dosing regimens for patients with an FFM < 50 kg for the most susceptible candida species (C. albicans and C. glabrata). For higher FFM, a loading dose of 70 or 100 mg, with a maintenance dose of 70 mg, reached AUC/MIC ratios for these species.

Conclusions: There is moderate penetration of caspofungin into the peritoneal cavity (33%). For empirical treatment, a dose escalation of 100 mg loading dose on the first day is suggested for higher FFM to ensure adequate concentrations into the abdominal cavity for the most susceptible candida species.