Clotrimazole

Unlike bacteria, yeasts and fungi are eukaryotes, as are humans (and all other plants and animals). The basic structure of a fungal cell is nearly identical to a human's. This means finding a target for an antifungal to attack, that does not exist in the infected organism, is more difficult.

The imidazole (eg. clotrimazole, miconazole and ketoconazole) and triazole (eg. fluconazole) groups of antifungal drugs inhibit the enzyme cytochrome P450 14α;;-demethylase. This enzyme converts lanosterol to ergosterol, and is required in fungal cell wall synthesis. These drugs also block steroid synthesis in humans. Active against Candida albicans and used for vaginal and vulval candidiasis (‘thrush’).

Antifungal drugs are used to treat superficial fungal infections such as athlete's foot, ringworm and candidiasis (thrush), as well as serious systemic infections like cryptococcal meningitis. Clotrimazole, econazole, fenticonazole, sulconazole, and tioconazole are used for the local treatment of vaginal candidiasis and for dermatophyte infections.

Ketoconazole is rarely used now but is better absorbed by mouth than other imidazoles and is used for systemic treatment but carries a real risk of liver damage and should not be used for superficial fungal infections. Miconazole can be used locally for oral infections; it is also effective in intestinal infections. Nail dermatophyte infections respond best to systemic therapy with terbinafine.

Triazole antifungals are newer, and are less toxic systemically and more effective. They are closely related in structure and include fluconazole, itraconazole and voriconazole. Fluconazole is very well absorbed after oral administration. It also achieves good penetration into the cerebrospinal fluid as is used to treat fungal meningitis.