Fast and Sensitive Analysis of Fosfomycin in Human Plasma Microsamples Using Liquid Chromatography–Tandem Mass Spectrometry for Therapeutic Drug Monitoring

Abstract

Background: Fosfomycin is an antibiotic recently repurposed as a potential combination treatment for difficult-to-treat Gram-negative bacterial infections. The pharmacokinetic features of fosfomycin have demonstrated that different pathophysiologic alterations may affect its exposure. Therapeutic drug monitoring may improve real-time management of fosfomycin therapy in different clinical scenarios. Objectives: To develop and validate a fast and sensitive liquid chromatography – tandem mass spectrometry method for measuring fosfomycin in human plasma microsamples (3 µL). Methods: Analysis was preceded by a user-friendly pre-analytical single-step process performed via a rapid chromatographic run of 2.5 minutes, followed by negative electrospray ionization and detection on a high-sensitivity triple quadrupole tandem mass spectrometer operated in the multiple reaction monitoring mode. European Medicines Agency guidelines were used to validate the specificity, sensitivity, linearity, precision, accuracy, matrix effects, extraction recovery, limits of quantification, and stability of the analytical method. Results: The new assay produced accurate (BIAS%: 0.9–9.1) and precise (coefficient of variation [CV]%: 8.1–9.5) measurements of fosfomycin over a concentration range of 1–1000 mg/L. Overall, analyte recovery was consistent (mean values: 91.2%–97.2%) at all tested concentration levels. The analyte was also stable in human plasma and the final extract under various storage conditions. The clinical applicability of the assay was confirmed through quantitation of plasma samples obtained from patients. Conclusions: A sensitive liquid chromatography – tandem mass spectrometry method for measuring fosfomycin in plasma was developed and validated according to the European Medicines Agency criteria. Quantitation of fosfomycin in clinical plasma samples confirmed that the assay is suitable for therapeutic drug monitoring in clinical scenarios.