Variability of pharmacokinetic parameters in patients receiving different dosages of daptomycin: is therapeutic drug monitoring necessary?

Pharmacokinetic studies of daptomycin in septic patients indicate that pharmacokinetic parameters may be altered. The purpose of this clinical investigation is to determine the pharmacokinetics of daptomycin in a population of hospitalized patients with clinically significant gram-positive infections and receiving daptomycin. Daptomycin was measured using an isocratic HPLC technique. Thirty-five patients suffering from gram-positive severe infections and receiving daptomycin were included in the study. Patients were divided into two groups, depending on the dose of daptomycin received: group A, including 24 patients receiving 6 mg/kg/day daptomycin and group B, 11 patients receiving 8 mg/kg/day. Patients receiving a daptomycin dosage of 8 mg/kg/day had significantly higher values of mean C (max) and AUC(0-24). Each group was further divided into three subgroups, according to the creatinine clearance (CrCl) values: (1) patients with a CrCl > 80 ml/min, (2) patients with CrCl ranging between 80 and 40 ml/min, and (3) patients with CrCl < 40 ml/min. Compared to patients with normal renal function, those with CrCl < 40 ml/min had higher mean values of minimum concentration (C (min)) (p < 0.001), AUC(0-24) (p = 0.03), and prolonged plasma half-time (p < 0.001). These differences were present both in patients receiving 6 and those with 8 mg/kg/day. However, in each of the three subgroups with different degrees of renal function a marked variability of pharmacokinetics parameters was observed. The factors associated with increased mortality were an infection acquired in the ICU, hypoalbuminemia, and AUC/MIC < 666. The marked variability that characterizes daptomycin pharmacokinetics in these patients suggest the monitoring of the main pharmacokinetic parameters in this clinical setting.