Clinical use of systemic antifungal agents

The chemistry, pharmacology, pharmacokinetics, clinical uses, adverse effects, and drug interactions of amphotericin B, flucytosine, ketoconazole, and miconazole are reviewed. Amphotericin B, a heptaene compound with poor water solubility, disrupts the fungal cell wall by binding to ergosterol. Ketoconazole and miconazole, imidazole derivatives, are poorly water soluble and inhibit the synthesis of ergosterol. Flucytosine is a readily water-soluble, fluorinated pyrimidine agent that may be metabolized to fluorouracil. The pharmacokinetics of amphotericin B is unique and has not yet been clearly defined. After oral administration, absorption of flucytosine from the gastrointestinal tract is rapid and nearly complete. In adults, oral administration of ketoconazole produces peak concentrations of drug one to two hours after the dose. Miconazole is administered only intravenously and distributes well into most tissues. Amphotericin B remains the drug of choice for most systemic mycoses. Dosing of amphotericin B is often empiric and patient specific. Flucytosine is rarely used alone; the combination of flucytosine and amphotericin B exerts synergistic killing of many fungi. Ketoconazole is effective for treating many chronic fungal infections. Miconazole is seldom used because of the availability of agents that are equally effective, less toxic, or both. Nephrotoxicity can occur with amphotericin B therapy, while flucytosine is associated with gastrointestinal and hematologic toxicities. Ketoconazole is much less toxic than any of the other agents, while miconazole has a high incidence of adverse effects. In addition to the need for more effective and less toxic agents, research is needed to clearly define the pharmacokinetics and pharmacodynamics of currently available antifungal drugs.