Development and validation of an ultra performance liquid chromatography-tandem mass spectrometry method for the quantification of daptomycin in human plasma.

A rapid, simple and accurate analytical method based on ultra performance liquid chromatography (UPLC) combined with electrospray ionization (ESI) tandem mass spectrometry (MS/MS) on a hybrid q TOF instrument has been developed and fully validated for the quantification of daptomycin (DPT) in human plasma. The samples were analyzed after simple pretreatment involving protein precipitation, while chromatographic separation of DPT and the internal standard (reserpine) was achieved on an Acquity BEH C18 column (100 mm × 2.1 mm, 1.7 μm) using gradient elution with 0.1% aqueous formic acid (FA) and acetonitrile with 0.1% FA (with DPT eluting at 2.60 min). The method presented good fit (r>0.999) over the quantification range of 0.01-10 μg mL⁻¹ with the lower limit of quantitation (LLOQ) being 0.01 μg mL⁻¹ of human plasma for DPT. The intra- and inter-day precision, measured as % relative standard deviation, was less than 11% for DPT. The validation results showed that the developed method demonstrated adequate selectivity, sensitivity, precision and accuracy and therefore was successfully applied to the analysis of clinical samples following intravenous (iv) administration of 5.4 mg kg⁻¹ DPT to patients suffering from post-traumatic osteomyelitis induced by methicillin-resistant Staphylococcus aureus (MRSA). The developed methodology is the first report of an accurate mass tandem MS method for the analysis of this potent antibiotic in human plasma and can be used to further study pharmacokinetic, bioequivalence and even metabolic aspects related to this drug.