Echinocandins

ECHINOCANDINS

Chemistry & Pharmacokinetics

Echinocandins are the newest class of antifungal agents to be developed. They are large cyclic peptides linked to a long-chain fatty acid. Caspofungin, micafungin, and anidulafungin are the only licensed agents in this category of antifungals, although other drugs are under active investigation. These agents are activeagainst Candida and Aspergillus, but not C neoformans or the agents of zygomycosis and mucormycosis.

Echinocandins are available only in intravenous formulations. Caspofungin is administered as a single loading dose of 70 mg, followed by a daily dose of 50 mg. Caspofungin is water soluble and highly protein-bound. The half-life is 9–11 hours, and the metabolites are excreted by the kidneys and gastrointestinal tract. Dosage adjustments are required only in the presence of severe hepatic insufficiency. Micafungin displays similar properties with a half-life of 11–15 hours and is used at a dose of 150 mg/d for treatment of esophageal candidiasis, 100 mg/d for treatment of candidemia, and 50 mg/d for prophylaxis of fungal infections. Anidulafungin has a half-life of 24–48 hours. For esophageal candidiasis, it is administered intravenously at 100 mg on the first day and 50 mg/d thereafter for 14 days. For candidemia, a loading dose of 200 mg is recommended with 100 mg/d thereafter for at least 14 days after the last positive blood culture.

Mechanism of Action

Echinocandins act at the level of the fungal cell wall by inhibiting the synthesis of β(1–3)-glucan (Figure 48–1). This results in dis-ruption of the fungal cell wall and cell death.

Clinical Uses & Adverse Effects

Caspofungin is currently licensed for disseminated and mucocuta-neous candidal infections, as well as for empiric antifungal therapy during febrile neutropenia, and has largely replaced amphotericin B for the latter indication. Of note, caspofungin is licensed for use in invasive aspergillosis only as salvage therapy in patients who have failed to respond to amphotericin B, and not as primary therapy. Micafungin is licensed for mucocutaneous candidiasis, candidemia, and prophylaxis of candidal infections in bone marrow transplant patients. Anidulafungin is approved for use in esophageal candidi-asis and invasive candidiasis, including candidemia.

Echinocandin agents are extremely well tolerated, with minor gastrointestinal side effects and flushing reported infrequently. Elevated liver enzymes have been noted in several patients receiving caspofungin in combination with cyclosporine, and this combina-tion should be avoided. Micafungin has been shown to increase levels of nifedipine, cyclosporine, and sirolimus. Anidulafungin does not seem to have significant drug interactions, but histamine release may occur during intravenous infusion.