Development and validation of a UPLC-MS/MS method for simultaneous quantification of polymyxins and caspofungin in human plasma for therapeutic drug monitoring

Objective: To develop a rapid, convenient, accurate, and low-residual-effect ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the determination of polymyxin B sulfate and colistin sulfate in the blood of patients with multidrug-resistant bacterial infections, as well as caspofungin acetate in the blood of patients with fungal infections, thus facilitating the rational use of antibiotics in clinical applications.

Methods: All analytes were diluted with 0.2 % aqueous formic acid, and plasma proteins were precipitated using acetonitrile. The selected reaction monitoring (SRM) mode was used for measurement. Separation of all analytes was completed on a Hypersil GOLD C18 column (100 × 2.1 mm, 3.0 µm). They were quantitatively analyzed using electrospray ionization on a triple quadrupole mass spectrometer in the positive ion mode. The mobile phase consisted of water (containing 0.1 % formic acid) and acetonitrile, which was delivered by gradient elution at a flow rate of 0.3 ml/min. The internal standard was bacitracin zinc (BcZn), and the column temperature was maintained at 25 °C. The runtime for each analysis was 3.5 min.

Results: The procedure was validated following the recommendations of the U.S. Food and Drug Administration, which included measurements of accuracy (ranging from 83.27 % to 105.86 % for within-run and between-run accuracy), precision (with coefficients of variation from 2.50 % to 16.51 % for within-run precision and between-run precision), and matrix effects (ranging from 88.65 % to 103.94 %). The extraction recoveries ranged from 38.01 % to 42.76 for polymyxin B1 (PMB1), polymyxin B2 (PMB2), polymyxin E1 (PME1), polymyxin E2 (PME2), and 88.65 % to 89.84 % for caspofungin (CPF). Plasma samples were stable under various storage conditions, including three freeze-thaw cycles at -80 °C, 24-hour periods at room temperature and 4 °C, and 30 days of freezing at both -20 °C and -80 °C, with relative standard deviations (RSD) of less than 15 %.

Conclusion: In this study, a UPLC-MS/MS method was developed to simultaneously quantify PMB1, PMB2, PME1, PME2, and CPF in human plasma. The method was validated in blood samples from patients with multidrug-resistant bacteria combined with fungal infections and is suitable for therapeutic drug monitoring.