Teratological interaction between the bis-triazole antifungal agent fluconazole and the anticonvulsant drug phenytoin.

Previous studies implicated the cytochrome P450 (CYP) system as critical in the teratogenic bioactivation of phenytoin (PHT). Fluconazole (FCZ) is an antifungal bis-triazole with potent inhibitory effect on the principal CYP-dependent metabolic pathway of PHT. In this study an in vivo experimental model was used to evaluate the potential ability of FCZ (2, 10, or 50 mg/kg intraperitoneally) to modulate PHT (65 mg/kg intraperitoneally) teratogenesis on day 12 (plug day = day 1) Swiss mice. PHT alone elicited embryocidal and malformative effects, with cleft palate as the major malformation. Pretreatment with the nonembryotoxic dosage of 10 mg FCZ/kg potentiated PHT-induced teratogenesis, as indicated by a twofold (from 6.2% to 13.3%) increment of cleft palate incidence (P < 0.05). Combined treatment with 50 mg FCZ/kg plus PHT resulted in a statistically significant (P < 0.05) increment of the resorption incidence recorded after PHT-alone exposure, but possibly as a consequence of the increased embryolethality, in the loss of the potentiative effect on PHT teratogenesis. Although the mechanistic nature of teratological interaction between FCZ and PHT remains to be established, these results may not support CYP system-mediated metabolic conversion as the mechanistic component of PHT teratogenesis.