A mathematical model of the kinetics and tissue distribution of 2-fluoro-beta-alanine, the major catabolite of 5-fluorouracil.

2-Fluoro-beta-alanine (FBAL) is the major metabolite of 5-fluorouracil (FUra), one of the most widely used anticancer drugs. It has been suggested previously that FBAL and/or its metabolites may have a role in the hepatotoxicity, neurotoxicity and cardiotoxicity resulting from FUra chemotherapy. Studies in patients and experimental animals have demonstrated that FBAL has a prolonged elimination compared with the parent drug, FUra. In the present manuscript, a mathematical model is developed for the kinetics and tissue distribution of FBAL. This model is based on recently published data from a study of the pharmacokinetics and disposition of FBAL in rats (Zhang et al., Drug Metab Dispos 20: 113-119, 1992). Satisfactory agreement was achieved between predicted and measured values, permitting an accurate evaluation of the kinetic and distribution parameters for FBAL. This model indicates that: (1) FBAL accumulates in several tissues including brain, heart, spleen, and enterohepatic system; and (2) enterohepatic circulation of FBAL and its bile acid conjugates has an important role in FBAL kinetics and distribution as demonstrated by a model in which enterohepatic circulation parameters were deleted.