Development and validation of a liquid chromatography/tandem mass spectrometry method for determination of caspofungin in dried blood spots.

RATIONALE: A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for quantification of caspofungin in dried blood spots (DBS) was developed and validated. METHODS: The DBS samples were prepared by spotting whole blood onto Whatman 903 filter paper, drying at room temperature and extracting with 50% methanol and further cleaned by protein precipitation with acetonitrile. Roxithromycin was selected as internal standard, and the separation of the analytes with endogenous ingredients was accomplished on a Hypersil GOLD aQ column with a mobile phase composed of 0.1% formic acid (v/v) and methanol in gradient mode. The detection of the analytes was performed on a triple quadrupole mass spectrometer in positive electrospray ionization mode, and the following selective reaction monitoring (SRM) transitions were monitored: m/z 547.6 â†’ 538.7 and 837.4→ 679.4 for quantification of caspofungin and the internal standard, respectively. RESULTS: The total analytical time was 8 min for each run. The calibration curve exhibited a good linearity over the range from 0.2 to 20 µg/mL and the lower limit of quantification (LLOQ) was 0.2 µg/mL for caspofungin in DBS. The recoveries of caspofungin ranged from 62.64% to 76.69%, and no obvious matrix effect was observed. The intra- and inter-day precision and accuracy were within acceptable limits, and caspofungin in DBS was stable after storage at room temperature for 24 h and at -80°C for 30 days. There was no evident effect of the hematocrit value on the analysis of caspofungin. CONCLUSIONS: The proposed method presents an alternative to the conventional venous sampling method, and was successfully utilized for pharmacokinetics study of caspofungin in ICU patients.