Pharmacokinetics

The mean (SD) pharmacokinetic parameters of daptomycin at steady-state following IV administration of 4 to 12 mg/kg q24h to healthy young adults are summarized in Table 1.

Daptomycin pharmacokinetics were generally linear and time-independent at doses of 4 to 12 mg/kg q24h. Steady-state trough concentrations were achieved by the third daily dose. The mean (SD) steady-state trough concentrations attained following administration of 4, 6, 8, 10, and 12 mg/kg q24h were 5.9 (1.6), 6.7 (1.6), 10.3 (5.5), 12.9 (2.9), and 13.7 (5.2) µg/mL, respectively.

Table 1. Mean (SD) CUBICIN Pharmacokinetic Parameters in Healthy Volunteers at Steady-State

Distribution

Daptomycin is reversibly bound to human plasma proteins, primarily to serum albumin, in a concentration-independent manner. The overall mean binding ranged from 90 to 93%.

In clinical studies, mean serum protein binding in subjects with CL_CR ≥ 30 mL/min was comparable to that observed in healthy subjects with normal renal function. However, there was a trend toward decreasing serum protein binding among subjects with CL_CR < 30 mL/min (87.6%), including those receiving hemodialysis (85.9%) and continuous ambulatory peritoneal dialysis (CAPD) (83.5%). The protein binding of daptomycin in subjects with hepatic impairment (Child-Pugh B) was similar to that in healthy adult subjects.

The volume of distribution at steady-state (V_ss) of daptomycin in healthy adult subjects was approximately 0.10 L/kg and was independent of dose.

Metabolism

In vitro studies with human hepatocytes indicate that daptomycin does not inhibit or induce the activities of the following human cytochrome P450 isoforms: 1A2, 2A6, 2C9, 2C19, 2D6, 2E1, and 3A4. In in vitro studies, daptomycin was not metabolized by human liver microsomes. It is unlikely that daptomycin will inhibit or induce the metabolism of drugs metabolized by the P450 system.

In 5 healthy young adults after infusion of radiolabeled ¹⁴C-daptomycin, the plasma total radioactivity was similar to the concentration determined by microbiological assay. In a separate study, no metabolites were observed in plasma on Day 1 following administration of CUBICIN at 6 mg/kg to subjects. Inactive metabolites have been detected in urine, as determined by the difference in total radioactive concentrations and microbiologically active concentrations. Minor amounts of three oxidative metabolites and one unidentified compound were detected in urine. The site of metabolism has not been identified.

Excretion

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