Background: Higher daptomycin doses are advocated for select methicillin-resistant Staphylococcus aureus (MRSA)-related infections, but the probabilities of target attainment (PTA) and toxicity of these doses have not been characterized in critically ill patients.
Methods: We evaluated the plasma pharmacokinetics (PK) and clinical outcomes of a cohort of critically ill patients treated with daptomycin 6-8 mg/kg/day for primarily Staphylococcus species-related infections. Daptomycin concentrations were measured intensively over the initial 96-hour dosing period. Data were modeled by population PK analyses, and Monte Carlo simulation was used to estimate the probabilities of effect and toxicity with standard and alternate dosing regimens.
Results: Fifty patients with a mean (SD) age of 69.7 (12.2) years, weight 74.5 (20.3) kg, and creatinine clearance 56.8 (38.2) mL/minute were enrolled with measurements of 12 (2.2) daptomycin samples per patient. Significantly lower daptomycin exposures were observed despite comparable doses in a subset of patients (n = 13) with augmented clearance (CL). No covariates of CL were identified, but this subset was significantly more likely to be in severe sepsis or septic shock, have higher Sequential Organ Failure Assessment scores, and MRSA bacteremia. In-hospital mortality was significantly higher (30.7% vs 10.8%) in patients with augmented daptomycin CL. Use of an empiric fixed dose of 750 mg of daptomycin is predicted to achieve a comparable PTA with a lower probability of toxicity as compared to the use of 10 mg/kg in critically ill patients.
Conclusions: A reappraisal of current daptomycin dosing recommendations is needed to improve the PTA and reduce toxicity among critically ill patients.
Keywords: critically ill; daptomycin; dosing; pharmacokinetics; sepsis.