Antifungal drugs, including fluconazole, itraconazole, micafungin, miconazole, and voriconazole, are widely used in the treatment of systemic candidal infections and mycoses. The mechanism of action of these antifungal drugs except for micafungin is the inhibition of fungal cytochrome P450 (CYP, 14a-sterol demethylase), an enzyme responsible for the conversion of lanosterol to 14a-demethyllanosterol in the ergosterol biosynthetic pathway, 1,2) whereas micafungin inhibits 1,3-b-D-glucan synthase, leading to disruption of growing fungal cell wall and death of the fungal cell. 3,4)Multiple drug therapy is a common therapeutic practice, particularly in patients with several diseases or conditions, and many drug-drug interactions involving metabolic inhibition are being reported. 5,6) Recently, we have demonstrated that itraconazole and miconazole, as well as ketoconazole, had higher inhibitory effects on CYP3A4 metabolic activities than fluconazole and micafungin.7) In addition, the K i values of fluconazole and micafungin against nifedipine oxidation activity, a marker enzyme activity of CYP3A4, have been reported to be 10.7 mM and 17.3 mM, respectively. 8) Zhang et al. 9) reported that miconazole inhibits several CYPs, including CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4, with K i values ranging from 0.01 to 7.3 mM. Furthermore, it is likely that fluconazole and voriconazole inhibit CYP2C9, CYP2C19, and CYP3A4.2,10-13) On the other hand, fluconazole and itraconazole are reported to exhibit no inhibition of CYP2E1, whereas the K i value of miconazole against CYP2E1 activity is 4 mM. 14) However, there are few studies comparing the effect of antifungal drugs on the drugmetabolizing activity by human hepatic CYPs, such as CYP1A2, CYP2D6, and CYP2E1, under the same experimental conditions.Many inhibitors are known to be activated metabolically to a reactive intermediate(s) that, in turn, is irreversibly or quasi-irreversibly bound to the enzyme(s).15) For example, some acetylenes, including those synthetic steroids such as gestodene and ethinyl estradiol, cause mechanism-based inactivation of CYP3A4.16) Sorivudine is converted by gut flora to (E)-5-(2-bromovinyl)uracil (BVU), which is metabolized to dihydro-BVU by dihydropyrimidine dehydrogenase (DPD), and the dihydro-BVU binds to DPD itself.17) Numerous laboratories have indicated that these mechanism-based inactivators exhibit preincubation time-dependence of inhibition. [16][17][18][19][20][21][22][23][24][25][26][27] In the present study, we compared the effects of five antifungal drugs on specific activities by CYP1A2, CYP2D6, and CYP2E1 in human liver microsomes under the same experimental conditions. In addition, the effect of preincubation was estimated in order to investigate whether these antifungal drugs are the mechanism-based inhibitors. ) and itraconazole from Janssen-Kyowa (Tokyo, Japan). 7-Ethoxyresorufin, resorufin, debrisoquine sulfate, and chlorzoxazone were obtained from Sigma Chemical Co. (St. Louis, MO, U.S.A.). 4-Hydroxydebrisoquine ...