Validated high performance liquid chromatography–UV detection method for the determination of daptomycin in human plasma

Daptomycin is the first approved member of the new class cyclic lipopeptide antibiotic drugs, effective against a broad spectrum of Gram-positive bacteria. Here we present an HPLC method with UV detection capable to obtain pharmacokinetic data of daptomycin in human plasma, exemplarily shown in a critically ill patient with acute renal failure undergoing extended daily dialysis. Sample preparation consists only of protein precipitation with methanol. Chromatographic separation was achieved on a Zorbax Eclipse XDB-C8 column and daptomycin was detected at 224 nm. The calibration function was linear over the range from 3.5 to 350 μg/ml. The relative standard deviations were < 2% in the intra-day and < 6% in the inter-day measurements. The accuracy was always better than 7%. Daptomycin was stable in aqueous solutions for 2 months frozen at–20 °C. However, in plasma frozen at −20 °C a loss of 25% in 1 month was observed.