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A validated method for the quantification of fosfomycin in human plasma by liquid chromatography-tandem mass
Jens Martens-Lobenhoffer1, Stefanie M Bode-Böger1
1Institute of Clinical Pharmacology, Otto-von-Guericke University, Magdeburg, Germany.
Abstract:
Fosfomycin is a small, hydrophilic antibiotic drug with activity against Gram-positive as well as Gram-negative pathogens. It is in increasing use in intensive care units as a last line antibiotic since it shares no cross-resistance with other antibiotics. It is not metabolized and plasma levels are dependent on renal excretion rate and renal replacement therapy such as hemofiltration or hemodialysis. Measurement of fosfomycin plasma concentrations is therefore highly desirable in order to optimize dosing. We have developed a method for the quantification of fosfomycin in human plasma using HILIC chromatography on a silica stationary phase and tandem mass spectrometric detection. Sample preparation consisted only of protein precipitation without derivatization. Propylphosphonic acid was used as internal standard. Two calibration ranges from 15 to 150μg/ml and 100 to 750μg/ml were necessary to cover the whole range of plasma concentrations expected from intensive care patients. Intraday precision ranged from 4.0% to 6.4%, depending on the concentration level, with accuracies ranging from -1.1% to 11.5%. The corresponding interday precisions and accuracies were 2.0-11.0% and 0.6-7.8%, respectively. Fosfomycin was stable in human plasma under all storing conditions relevant for clinical samples. First experiences with this method in clinical routine use confirmed the applicability and ruggedness of the analytical procedure.
Insights
Accurate measurement of fosfomycin in intensive care patients is crucial for optimizing antibiotic dosing. A new HILIC-MS/MS method quantifies fosfomycin in plasma, ensuring stability and clinical applicability.
Area of Science:
- Pharmacology
- Analytical Chemistry
- Clinical Pharmacy
Background:
- Fosfomycin is a critical last-line antibiotic for Gram-positive and Gram-negative infections.
- Its efficacy is challenged by variable plasma levels influenced by renal function and replacement therapies.
- Optimized dosing requires precise measurement of fosfomycin concentrations in patient plasma.
Purpose of the Study:
- To develop and validate a robust analytical method for quantifying fosfomycin in human plasma.
- To ensure the method is suitable for routine clinical use in intensive care settings.
Main Methods:
- Hydrophilic Interaction Liquid Chromatography (HILIC) on a silica stationary phase.
- Tandem Mass Spectrometric (MS/MS) detection for sensitive and specific quantification.
- Simple protein precipitation for sample preparation without derivatization.
- Use of propylphosphonic acid as an internal standard.
Main Results:
- The method demonstrated high precision (intraday: 4.0–6.4%, interday: 2.0–11.0%) and accuracy (intraday: -1.1–11.5%, interday: 0.6–7.8%).
- Two calibration ranges (15–150 μg/ml and 100–750 μg/ml) covered therapeutic concentrations.
- Fosfomycin stability was confirmed in plasma under relevant clinical storage conditions.
Conclusions:
- A validated HILIC-MS/MS method allows for reliable quantification of fosfomycin in human plasma.
- This method supports therapeutic drug monitoring for optimizing fosfomycin dosage in intensive care patients.
- The procedure is applicable and robust for clinical routine use.
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