Human-relevant concentrations of the antifungal drug clotrimazole disrupt maternal and fetal steroid hormone profiles in rats

Clotrimazole is a non-prescription and broad-spectrum antifungal drug sold under brand names such as Canesten® and Lotrimin®. It is used to treat different types of fungal infections, from oral thrush to athlete's foot and vaginal mycosis. The level of exposure to clotrimazole is uncertain, as the exact usage amongst self-medicating patients is unclear. Recent studies have raised potential concern about the unsupervised use of clotrimazole during pregnancy, especially since it is a potent inhibitor of CYP enzymes of the steroidogenesis pathway. To address some of these concerns, we have assessed the effects of intrauterine exposure to clotrimazole on developing rat fetuses. By exposing pregnant rats to clotrimazole 25 or 75 mg/kg bw/day during gestation days 7-21, we obtained internal fetal concentrations close to those observed in humans. These in vivo data are in strong agreement with our physiologically-based pharmacokinetic (PBK)-modelled levels. At these doses, we observed no obvious morphological changes to the reproductive system, nor shorter male anogenital distance; a well-established morphometric marker for anti-androgenic effects in male offspring. However, steroid hormone profiles were significantly affected in both maternal and fetal plasma, in particular pronounced suppression of estrogens was seen. In fetal testes, marked up-concentration of hydroxyprogesterone was observed, which indicates a specific action on steroidogenesis. Since systemic clotrimazole is rapidly metabolized in humans, relevant exposure levels may not in itself cause adverse changes to the reproductive systems. Its capacity to significantly alter steroid hormone concentrations, however, suggests that clotrimazole should be used with caution during pregnancy.