An immunoassay method for the pharmacokinetics of 5-fluorouracil in patients with gastric cancer administered adjuvant chemotherapy.

Conventional gas chromatography-mass spectrometry (GC-MS) was compared with a new immunoassay method for measuring plasma (5-FU) concentrations in adjuvant chemotherapy with TS-1 for patients with gastric cancer. TS-1 was administered orally to patients after gastrectomy. Blood samples for pharmacokinetic analysis were collected on the seventh day of treatment. The mean area under the time concentration curve (AUC)(0-8), half-life (t(1/2)), and maximum drug concentration (C(max)) obtained by the two methods were as follows: GC-MS, 847.9 μg/ml/hr, 2.76 h, and 186.6 ng/ml; and immunoassay, 1311.2 μg/ml/hr, 3.5 h, and 259.8 ng/ml. Significant correlations were observed for AUC(0-8) (p=0.0001), C(max) (p=0.0007), and changes in the 5-FU concentration in blood over time (p=0.018) for the two methods. Compared with the conventional GC-MS method, the new immunoassay method provides similar results, but is simpler and results can be obtained earlier. This method will be useful for monitoring the 5-FU concentration in serum from patients with gastric cancer receiving TS-1.