Purpose: The effect of uridine (UR) coadministration on the intestinal metabolism from 5'-deoxy-5-fluorouridine (5'-DFUR) to 5-fluorouracil (5-FU) was evaluated by a method of concentration difference between portal and systemic bloods in conscious rats (PS method).
Methods: 5'-DFUR (100 mg/kg) alone (Group A), or 5'-DFUR + UR (100 mg/kg each) (Group B) was orally administered to conscious rats. The portal and arterial bloods were simultaneously withdrawn from two canulas at appropriate time intervals, and blood concentrations of 5'-DFUR, 5-FU, UR and uracil (U) were assayed by HPLC. The concentration-time profiles of these drugs and its metabolites were analyzed by local moment analysis.
Results: UR coadministration made the local absorption ratio (Fa) of 5'-DFUR decrease significantly from 60.1 +/- 10.5% to 38.0 +/- 18.6% of dose. Though the local absorption ratios (Fm(a)) of the metabolite (5-FU) were the same between Group A and Group B (8.3 +/- 1.9 and 8.7 +/- 4.0% of 5'-DFUR, respectively), AUC of arterial 5-FU in Group B was 5 times greater than that in Group A. UR was not detected in the portal blood, and Fm(a) of U was estimated to be 41.9 +/- 26.8% of UR in Group B.
Conclusions: It is predicted that a large portion of 5-FU generated from 5'-DFUR is further degraded in the intestine in Group A, and U generated from UR blocks 5-FU degradation in the intestine and the systemic circulation in Group B.