RT Journal Article SR Electronic T1 Prediction of In Vivo Drug-Drug Interactions Based on Mechanism-based Inhibition from In Vitro Data: Inhibition of 5-Fluorouracil Metabolism by (E)-5-(2-Bromovinyl)uracil JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 467 OP 474 VO 28 IS 4 A1 Kanamitsu, Shin-ichi A1 Ito, Kiyomi A1 Okuda, Haruhiro A1 Ogura, Kenichiro A1 Watabe, Tadashi A1 Muro, Kei A1 Sugiyama, Yuichi YR 2000 UL http://dmd.aspetjournals.org/content/28/4/467.abstract AB The fatal drug-drug interaction between sorivudine, an antiviral drug, and 5-fluorouracil (5-FU) has been shown to be caused by a mechanism-based inhibition. In this interaction, sorivudine is converted by gut flora to (E)-5-(2-bromovinyl)uracil (BVU), which is metabolically activated by dihydropyrimidine dehydrogenase (DPD), and the activated BVU irreversibly binds to DPD itself, thereby inactivating it. In an attempt to predict this interaction in vivo from in vitro data, inhibition of 5-FU metabolism by BVU was investigated by using rat and human hepatic cytosol and human recombinant DPD. Whichever enzyme was used, increased inhibition was observed that depended on the preincubation time of BVU and enzyme in the presence of NADPH and BVU concentration. The kinetic parameters obtained for inactivation represented by kinact andK′app were 2.05 ± 1.52 min−1, 69.2 ± 60.8 μM (rat hepatic cytosol), 2.39 ± 0.13 min−1, 48.6 ± 11.8 μM (human hepatic cytosol), and 0.574 ± 0.121 min−1, 2.20 ± 0.57 μM (human recombinant DPD). The drug-drug interaction in vivo was predicted quantitatively based on a physiologically based pharmacokinetic model, using pharmacokinetic parameters obtained from the literature and kinetic parameters for the enzyme inactivation obtained in the in vitro studies. In rats, DPD was predicted to be completely inactivated by administration of BVU and the area under the curve of 5-FU was predicted to increase 11-fold, which agreed well with the reported data. In humans, a 5-fold increase in the area under the curve of 5-FU was predicted after administration of sorivudine, 150 mg/day for 5 days. Mechanism-based inhibition of drug metabolism is supposed to be very dangerous. We propose that such in vitro studies should be carried out during the drug-developing phase so that in vivo drug-drug interactions can be predicted. The American Society for Pharmacology and Experimental Therapeutics