Ketoconazole. Mechanism of action, spectrum of activity, pharmacokinetics, drug interactions, adverse reactions and therapeutic use.

Ketoconazole is a well-tolerated oral antifungal agent with a broad spectrum of activity in vitro, but in vitro testing has not yet been correlated to in vivo results. In addition, many variables that can alter in vitro test results have been identified. The drug shows effectiveness in the treatment of paracoccidioidomycosis, chronic mucocutaneous candidiasis, oral thrush, coccidioidomycosis and histoplasmosis. It was recently approved for use in blastomycosis. It is not yet approved for use in dermatophyte infections, but a large body of literature exists supporting this application. Ketoconazole has several reported drug interactions, including lower bioavailability with cimetidine, accumulation of cyclosporin during concurrent therapy and a possible disulfiram-like reaction with alcohol. It is highly protein bound to albumin and is extensively metabolized. Dosage adjustment is not required in renal failure. The main side effects are gastrointestinal and occur in 5-10% of the patients. Rare side effects include gynecomastia and hepatotoxicity. The latter is reported to occur in 1 of 12,000 patients. Ketoconazole impairs testosterone synthesis, and therefore it is recommended that administration more than once daily be avoided in men. The usual dosage is 200-400 mg administered once daily. Few comparative or controlled studies have been published thus far. How it compares to amphotericin B is not known. The optimum dosage and the optimum duration of therapy are not established.