Gas chromatographic-mass spectrometric method for routine monitoring of 5-fluorouracil in plasma of patients receiving low-level protracted infusions.

A gas chromatographic-mass spectrometric (GC-MS) method is described which quantitates 5-fluorouracil (5-FU) plasma levels ranging from 0.5 to 50 ng/ml. The analysis uses two internal standards, 1,3-[15N2]-5-fluorouracil and 5-chlorouracil. Extraction and derivatization of the pyrimidine bases were accomplished in a single step using acetonitrile. Compounds were analyzed as their 1,3-dipentafluorobenzyl derivatives by electron-impact MS, and the GC-MS analysis was automated with respect to sample injection and data reduction. Stability of the analysis was demonstrated by continuous unattended analysis of 5-FU in human plasma for periods of up to three days with no deterioration of the quantitative results. The method is applicable to quantitating 5-FU plasma levels in patients receiving protracted infusions of the drug for colorectal cancer or other malignancies.