Plasma concentrations of 5-FU at 0, 0.5, 1, 2, 4, 8, 24 h were measured using negative ion chemical ionization gas chromatography mass spectrometry. Pharmacokinetic parameters including area under the curve (AUC0–24h), maximum concentration (Cmax), time taken to reach maximum concentration (Tmax), half-time (T1/2), area under the first moment curve (AUMC0–24h), mean resistance time (MRT0–24h), and plasma clearance (CL) were derived with non-compartmental methods using WinNonlin version 3.1 .