Evaluation of pharmacokinetics and the stability of daptomycin in serum at various temperatures

Background Daptomycin exhibits concentration-dependent antibacterial activity. By monitoring daptomycin serum concentrations, clinicians may be able to predict the effectiveness of treatments for infections more accurately. However, it has been reported that daptomycin concentrations in plasma samples stored at −20 °C decrease approximately 25% after 4 weeks. The aim of this study was to evaluate the stability of daptomycin in serum at various temperatures. Methods Daptomycin serum samples were prepared and stored at different temperatures. The stability of daptomycin under various conditions was evaluated by sequential measurements of concentration. Results Although the loss of concentration of daptomycin in serum samples stored in freezers (−80 °C and −20 °C) was less than 10% after 168 days (6 months), the concentrations in samples stored in a refrigerator (4 °C) decreased by more than 70% over the same period. Furthermore, daptomycin concentrations in serum samples stored at close to body temperature (35 °C, 37 °C, and 39 °C) decreased by more than 50% after only 24 h. Conclusions The results of the present study demonstrate that the measurement of serum concentrations of daptomycin needs to be performed rapidly. Furthermore, the degradation of daptomycin in serum may be involved in its elimination from the living body.