An LC-MS/MS method for quantification of daptomycin in dried blood spot: Application to a pharmacokinetics study in critically ill patients

An LC-MS/MS method for analysis of daptomycin in dried blood spot (DBS) was established. The DBS samples were prepared by spotting one droplet of blood onto absorbent paper, and were left to dry at room temperature. The DBS samples were extracted with water followed by deproteinization with acetonitrile. A Hypersil GOLD aQ column was applied to chromatographically separate the analyte, and mobile phase at a flow rate of 0.3 mL/min consisted of methanol and 0.1% formic acid. Detection of analyte was performed on a triple quadrupole mass spectrometer in positive mode, and the mass spectrometer was manipulated in selective reaction monitoring (SRM) mode. The SRM transitions m/z 810.9→811.1 and 810.9→640.8 for quantification and qualification of daptomycin and m/z 837.4→679.4 and 837.4→558.3 for roxithromycin used as internal standard were monitored. The calibration curves covering the range of 1–200 μg/mL exhibited good linearity, and lower limit of quantification (LLOQ) was 1 µg/mL for daptomycin in DBS. The proposed method was fully validated, and hematocrit effect on the quantification of daptomycin in DBS was not obvious. The proposed DBS method was non-invasive and required collection of a micro-volume blood, and was successfully utilized to a pharmacokinetics study in seriously ill patients.