title: Evaluation of pharmacokinetics and the stability of daptomycin in serum at various temperatures.
abstract: 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 168days (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 24h.
  
  
  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.
authors.affiliation: Department of Medical Pharmaceutics, Faculty of Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan.
authors.forename: Chika
authors.initials: C
authors.lastname: Ogami
authors.affiliation: Department of Medical Pharmaceutics, Faculty of Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan. Electronic address: ytsuji@pha.u-toyama.ac.jp.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tsuji
authors.affiliation: Department of Medical Pharmaceutics, Faculty of Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan; Certara G.K., Tokyo, Japan.
authors.forename: Hidefumi
authors.initials: H
authors.lastname: Kasai
authors.affiliation: Department of Pharmacy, National Hospital Organization Beppu Medical Center, Ooaza, Beppu, Oita, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Hiraki
authors.affiliation: Department of Clinical Infectious Diseases, Graduate School of Medicine and Pharmaceutical Sciences for Research, University of Toyama, Sugitani, Toyama, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Yamamoto
authors.affiliation: Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka, Japan.
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Matsunaga
authors.affiliation: Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka, Japan.
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Karube
authors.affiliation: Department of Medical Pharmaceutics, Faculty of Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama, 930-0194, Japan.
authors.forename: Hideto
authors.initials: H
authors.lastname: To
mesh_terms: D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics*; D017576:Daptomycin / Q000493:pharmacokinetics*; D004355:Drug Stability; D006801:Humans; D013696:Temperature
chemical_list: D000900:Anti-Bacterial Agents; D017576:Daptomycin
keywords: Daptomycin; Protease; Stability; Therapeutic drug monitoring