Roles of different CYP enzymes in the formation of specific fluvastatin metabolites by human liver microsomes.

Fluvastatin has been considered to be metabolised to 5-hydroxy fluvastatin (M-2), 6-hydroxy fluvastatin (M-3) and N-desisopropyl fluvastatin (M-5) in human liver microsomes by primarily CYP2C9. To elucidate the contribution of different CYP enzymes on fluvastatin metabolism, we examined the effect of CYP inhibitors and CYP2C-specific monoclonal antibodies on the formation of fluvastatin metabolites in human liver microsomes. Human liver microsomes were incubated with fluvastatin with or without pre-treatment with CYP inhibitors or monoclonal antibodies. Selective inhibitors of CYP2C9 (sulfaphenazole), CYP3A (ketoconazole) and CYP2C8 (quercetin) were employed and monoclonal antibodies were against CYP2C8, CYP2C9, CYP2C19 and CYP2C8/9/18/19. According to the amount of fluvastatin metabolites produced, the formation of M-3 was found to be major pathway of fluvastatin metabolism (the relative contribution was calculated to be more than 80%). Sulfaphenazole inhibited the formation of M-2 largely, but had little effect on the formation of M-3. It also inhibited the formation of M-5. Ketoconazole markedly inhibited the formation of M-3, but did not inhibit the formation of M-2 and M-5. Quercetin had a moderate inhibitory effect on the formation of all three fluvastatin metabolites. Monoclonal antibodies against CYP2C9 and CYP2C8/9/18/19 markedly inhibited the formation of M-2 and M-5. None of monoclonal antibodies showed clear inhibition on the formation of M-3. In contrast to previous published work, our results suggest that M-2 and M-5 are formed preferentially by CYP2C9, and that M-3 is mainly formed by CYP3A. In summary, the results contribute to a better understanding of the drug-drug interaction potential for fluvastatin in vivo.