Determination of Eniluracil and 5-Fluorouracil in Human Plasma by LC–MS/MS

BACKGROUND: 5-fluorouracil (5-FU) has been one of the most widely used chemotherapeutic agents to treat various tumors, and eniluracil (5-ethynyluracil or EU) is being developed as a novel modulator of 5-FU. RESULTS: A simple and sensitive LC-MS/MS method was developed for reliably quantifying both EU and 5-FU in human plasma. The method was validated for EU over a dynamic concentration range from 4.13 ng/ml (LOQ) to 1030 ng/ml and for 5-FU over a dynamic concentration range from 8.61 ng/ml (LOQ) to 1080 ng/ml. The analog, 5-bromouracil, was used as the internal standard for calibration curves and quantitation. Method validation has covered the scope of precision, accuracy, specificity, LOQ, linearity/range, freeze-thaw cycles, benchtop integrity/stability, storage stability, matrix effect, recoveries and so on, in accordance with US FDA bioanalytical method validation guidelines. CONCLUSIONS: The validated method has shown good applicability for clinical studies and may be used for other clinical trials that involve measuring the concentration of EU and 5-FU simultaneously in human plasma and potentially in other similar biological matrices.