Cross-Resistance of Clinical Isolates of Candida albicans and Candida glabrata to Over-the-Counter Azoles Used in the Treatment of Vaginitis

Antifungal drug resistance in Candida spp. continues to increase in response to the widespread application of triazole therapeutics among immunosuppressed patients. Azole-based over-the-counter (OTC) antifungal agents used to treat vaginitis have the potential to exacerbate this problem by contributing to the selection of highly resistant strains of Candida in otherwise healthy women. In this study, we show that fluconazole-resistant (MIC > 64 μg/mL) blood stream isolates of Candida albicans and Candida glabrata obtained from cancer patients were cross-resistant to the root drugs miconazole, clotrimazole, and tioconazole (found in several over-the-counter products), but remained susceptible to butoconazole. We also provide evidence that spontaneous mutants of Candida glabrata selected for resistance to clotrimazole were cross-resistant to other azole-based drugs, including fluconazole. Our findings demonstrate cross-resistance of Candida strains to fluconazole and OTC azole antifungals, and support the notion that OTC drugs can promote azole resistance in Candida spp.