Daptomycin Dosage Optimization in Renal Impairment Using Model-Informed Precision Dosing

Background: Daptomycin's efficacy and toxicity are closely related to its exposure, which can vary widely among individuals. The patient, a 59-year-old male with an estimated glomerular filtration rate (eGFR) of 12 mL/min/1.73 m² and a weight of 64 kg, was treated with 850 mg of daptomycin every other day for infective endocarditis caused by methicillin-resistant Staphylococcus aureus (MRSA). For patients with an estimated glomerular filtration rate of less than 30 mL/min/1.73 m², the dosing recommendations are not explicitly defined in the endocarditis guidelines. Subsequently, the pharmacology department was contacted to adjust the dosage. Methods: A population pharmacokinetic model developed by Dvorchik et al. was used for Bayesian estimation of the patient’s pharmacokinetic parameters. The 24-hour area under the curve (AUC24) of daptomycin was calculated at steady state using peak and trough plasma samples. Results: The minimum inhibitory concentration (MIC) of the MRSA strain was 0.25 mg/L. An AUC24/MIC ratio below 666 is associated with higher mortality risk, while an AUC24 above 939 h·mg/L correlates with increased risk of muscular toxicity. Initial AUC24 estimation was 1091 h·mg/L. Following a dosage reduction to 700 mg every other day, the AUC24 increased to 1600 h·mg/L. Further reduction to 500 mg every other day brought the AUC24 down to 750 h mg/L, with two subsequent measurements showing consistent AUC24 values of 500 h·mg/L, which is within the target range. Conclusions: Daptomycin ended 6 weeks after the initial negative blood culture, with no adverse effects or recurrence of MRSA infection. This case underscores the need for therapeutic drug monitoring and a multidisciplinary approach to adjust daptomycin doses in patients with renal impairment.