Simple and Rapid Quantification of the Multi-Enzyme Targeting Antifolate Pemetrexed in Human Plasma

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BACKGROUND: Pemetrexed is an antifolate cytostatic drug that targets multiple enzymes involved in folate biosynthesis and is indicated for treatment of non-small-cell lung cancer and malignant pleural mesothelioma. As evidence for an exposure-response/toxicity relationship is accumulating, dose individualization using therapeutic drug monitoring may be a feasible strategy to optimize treatment. The purpose of this study was to develop a simple, sensitive, high-performance liquid chromatography method with UV detection for quantification of pemetrexed levels in human plasma. METHOD: The method involves a simple protein precipitation, followed by ultra-performance liquid chromatography with ultraviolet detection at a wavelength of 254 nm. Pemetrexed was separated using a mobile phase with a linear gradient and a run time of only 7 minutes. RESULTS: The assay has been validated over the concentration range 0.25-500 mg/L of pemetrexed. Accuracy for this assay ranged from -4.50% to 1.78%, and the within- and between-run coefficients of variation were <3.57%. Pemetrexed in plasma was proven to be stable for 8 months at -40 degrees C. CONCLUSIONS: The bioanalytical method we developed proved to be simple, accurate, precise, and fast. This analytical method is successfully in use for therapeutic drug monitoring and will be used for pharmacokinetic studies.