title: Development of a high-performance liquid chromatography method for the determination of caspofungin with amperometric detection and its application to in vitro microdialysis experiments.
abstract: Microdialysis is an increasingly employed technique for the determination of tissue pharmacokinetics. A high-performance liquid chromatography method for the quantitative determination of caspofungin in human microdialysates with amperometric detection is described. Since microdialysis of caspofungin is performed with a 100,000 molecular mass cut-off membrane, microdialysates contain protein that was precipitated at pH 4 with acetonitrile. Addition of 1-propanol (33%, v/v) to the sample extract improved the analytical recovery to 81-89%. Caspofungin and the internal standard clarithromycin were separated isocratically on a cyanopropyl silica column using acetonitrile-0.05 M citrate (33:67, v/v), adjusted to an apparent pH of 6.9, at a flow rate of 1.0 ml/min, and amperometric detection at +950 mV oxidation potential. Within-day and between-day imprecision and inaccuracy were <11%. The lower limit of quantification was 0.07 microg/ml. The method was applied to in vitro microdialysis experiments. Ringer's solution containing 1% (w/v) human albumin was used for the perfusing and surrounding medium, respectively. Albumin did not entirely prevent adsorption of caspofungin to the surface of membrane and/or tubing. When the binding-sites were saturated with albumin plus caspofungin prior to the start of sampling, the percentage of drug appearing in the microdialysate ("recovery") remained stable over the concentration range tested.
authors.affiliation: Department of Clinical Pharmacology, Division of Clinical Pharmacokinetics, Medical University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria. friederike.traunmueller@meduniwien.ac.at
authors.forename: Friederike
authors.initials: F
authors.lastname: Traunmüller
authors.forename: Ilka
authors.initials: I
authors.lastname: Steiner
authors.forename: Markus
authors.initials: M
authors.lastname: Zeitlinger
authors.forename: Christian
authors.initials: C
authors.lastname: Joukhadar
mesh_terms: D000077336:Caspofungin; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D004355:Drug Stability; D054714:Echinocandins; D004563:Electrochemistry; D055666:Lipopeptides; D017551:Microdialysis; D010456:Peptides, Cyclic / Q000032:analysis*
chemical_list: D054714:Echinocandins; D055666:Lipopeptides; D010456:Peptides, Cyclic; D000077336:Caspofungin