Development and validation of a simultaneous extraction procedure for HPLC-MS quantification of daptomycin, amikacin, gentamicin, and rifampicin in human plasma.

A simultaneous extraction method to measure daptomycin, amikacin, gentamicin, and rifampicin in human plasma, by high-performance liquid chromatography, was developed and validated. The method involved a rapid sample preparation by protein precipitation with acetonitrile followed by direct injection into a high-performance liquid chromatography system coupled with mass detection. Drug retention times were 10.00 +/- 0.25, 2.00 +/- 0.25, 3.50 +/- 0.25, 11.50 +/- 0.25, and 12.50 +/- 0.25 min for daptomycin, amikacin, gentamicin, rifampicin, and quinoxaline, respectively. Good linearity (mean r(2) = 0.998) was obtained for all drugs quantified over the range of clinically relevant concentrations in human plasma and the use of the internal standard quinoxaline improves accuracy (RSD% <14.9%) and intra-day (RSD% <11.56) and inter-day (RSD% <12.10) precision for the analytical procedure. The limits of quantification for daptomycin, amikacin, gentamicin, and rifampicin were 1.56, 2.34, 0.63, 0.63 microg/ml, respectively. Moreover, the addition of ion pair trifluoroacetic acid in the sample allowed the majority of gentamicin and amikacin separation. A rapid, specific, sensitive, accurate, and reproducible HPLC method was developed and validated to measure daptomycin, amikacin, gentamicin, and rifampicin in human plasma. This method is suitable for clinical pharmacokinetic studies.