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.

We have developed and validated a high-performance liquid chromatography method coupled with a mass detector to quantify itraconazole, voriconazole, and posaconazole using quinoxaline as the internal standard. The method involves protein precipitation with acetonitrile. Mean accuracy (percent deviation from the true value) and precision (relative standard deviation percentage) were less than 15%. Mean recovery was more than 80% for all drugs quantified. The lower limit of quantification was 0.031 g/ml for itraconazole and posaconazole and 0.039 g/ml for voriconazole. The calibration range tested was from 0.031 to 8 g/ml for itraconazole and posaconazole and from 0.039 to 10 g/ml for voriconazole.The incidence of mycoses has continued to increase over the past 2 decades, especially in immunocompromised patients. Notwithstanding the fact that in the last decades new antifungal agents have been approved, there is still a therapeutic need for azole compounds, such as itraconazole (ITC), posaconazole (PSC), and voriconazole (VRC), which inhibit 14a-demethylase, a key enzyme in the ergosterol biosynthesis of yeasts and molds (40).Antifungal prophylaxis, empirical therapy, and treatment of established fungal infections in the hematology patient population may be associated with significant toxicity or drug interactions, leading to subtherapeutic antifungal drug concentrations and poorer clinical outcomes (47). For example, a relationship between plasma concentrations and antifungal efficacy was shown for ITC (19), and the ratio between the area under the concentration-time curve (AUC) and MIC was identified to be predictive for the treatment efficacy of voriconazole and posaconazole, as well (1, 2). Antifungal therapeutic drug monitoring (TDM) could be an important tool in clinical practice if compliance is poor, the therapeutic window is narrow, or drug interactions and toxicity are common adverse effects. Therefore, quantification of drug in plasma samples is an important issue in clinical practice to improve efficacy and to decrease toxicity.Many methods to individually quantify ITZ (6,7,9,17,18,26,[31][32][33][34]37,45,46), PSC (8,35,39), and VRC (11,20,24,25,28,29,36,38) in human plasma have been published. Only one method described the quantification of the three triazoles plus fluconazole, ITC metabolite, and ketokonazole in human plasma using a solid-phase extraction procedure.The aim of this study was to develop and validate a high-performance liquid chromatography-mass spectrometry (HPLC-MS) method useful in routine TDM for quantitation of ITC, PSC, and VRC in human plasma using a protein precipitation extraction procedure and direct injection in an HPLC system. MATERIALS AND METHODSChemicals. ITC and dimethyl diquinoxaline (QX), used as the internal standard (IS), were purchased from Sigma Aldrich (St. Louis, MO), and PSC and VRC were purchased from Sequoia Research (Pangbourne, United Kingdom). Acetonitrile (HPLC grade) and methanol (HPLC grade) were purchased from J.T. Baker (Deventer, Holland). Formic aci...