Amphotericin B (AB) is used to treat serious fungal infections. Because there is a very real potential for severe toxicity associated with this drug, it should only be used for potentially fatal fungal infections that have not responded to less toxic treatment. Veterinary use of amphotericin has been primarily in dogs, but horses have been treated successfully. This article contains information on the use of this antifungal in horses.

Though usually fungistatic, it can be fungicidal against some organisms in high enough doses. Amphotericin B is active against a variety of fungal organisms, including

• Blastomyces,
• Aspergillus,
• Paracoccidiodes,
• Coccidiodes,
• Histoplasma,
• Cryptococcus,
• Mucor,
• Sporothrix
• Zygomycetes and Aspergillus is reportedly variable in its response to amphotericin.

AB is not well absorbed following oral administration so must be given parenterally to achieve sufficient concentrations to treat systemic fungal infections. After intravenous injection, the drug does not penetrate well into the pancreas, muscle, bone, aqueous humor, pleural, pericardial, synovial, or peritoneal fluids. The drug does enter the pleural cavity and joints when inflamed. CSF levels are approximately 3% of those found in the serum. The drug has been used successfully in the treatment of pneumonia, joint, and skin infections with fungi. The drug has also been used topically, injected directly into fungal lesions, and intrarticularly.