Ketoconazole is an azole antifungal. Ketoconazole was the first broad-spectrum oral antifungal agent available to treat systemic and superficial mycoses. Evidence of hepatotoxicity associated with its use emerged within the first few years of its approval. Due to its hepatotoxic side effects, oral ketoconazole was withdrawn from the European and Australian markets in 2013. The United States imposed strict relabeling requirements and restrictions for prescription, with Canada issuing a risk communication echoing these concerns. Today, oral ketoconazole is only indicated for endemic mycoses, where alternatives are not available or feasible. Meanwhile, topical ketoconazole is effective, safe, and widely prescribed for superficial mycoses, particularly as the first-line treatment for tinea versicolor. Topically administered ketoconazole is usually prescribed for fungal infections of the skin and mucous membranes, such as athlete's foot, ringworm, candidiasis (yeast infection or thrush), jock itch, and tinea versicolor. Topical ketoconazole is also used as a treatment for dandruff (seborrheic dermatitis of the scalp) and for seborrheic dermatitis on other areas of the body, perhaps acting in these conditions by suppressing levels of the fungus Malassezia furfur on the skin. Ketoconazole interacts with 14-α demethylase, a cytochrome P-450 enzyme necessary for the conversion of lanosterol to ergosterol. This results in inhibition of ergosterol synthesis and increased fungal cellular permeability. Other mechanisms may involve the inhibition of endogenous respiration, interaction with membrane phospholipids, inhibition of yeast transformation to mycelial forms, inhibition of purine uptake, and impairment of triglyceride and/or phospholipid biosynthesis. Ketoconazole can also inhibit the synthesis of thromboxane and sterols such as aldosterone, cortisol, and testosterone. Ketoconazole is active against clinical infections with Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum, Paracoccidioides brasiliensis.