Amphotericin B

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Amphotericin B

By: Dr. Dawn Ruben

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Overview

Amphotericin B belongs to a class of drugs known as macrolide antifungal agents. These drugs are used to treat serious fungal infections. As with other macrolide antifungals, amphotericin B binds to the cell membrane of certain fungi (those containing sterols) and allows important electrolytes to leak out, resulting in cell death.

Amphotericin B is produced by the bacteria Streptomyces nodosus. It is not effective against viral, bacteria or rickettisial infections.

The use of amphotericin B is very hard on the kidneys and some kidney damage is expected whenever amphotericin B is administered. For this reason, pets are typically hospitalized on intravenous fluids during treatment.

Amphotericin B is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.

This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.

Brand Names and Other Names

This drug is registered for use in humans only.

Human formulations: Fungizone® (Bristol-Myers Squibb), Amphotericin B® (Pharma-Tek), Abelcet® (Liposome Co.), Amphotec® (Sequus Pharmaceuticals) and AmBisome® (Fujisawa)

Veterinary formulations: None

Use of Amphotericin B

Amphotericin B is used to treat progressing and potentially fatal fungal infections. Most commonly, amphotericin B is used in combination with other drugs to treat blastomycosis, cryptococcosis and histoplasmosis.

Precautions and Side Effects

While generally safe and effective when prescribed by a veterinarian, amphotericin B can cause side effects in some animals.

Amphotericin B should not be used in animals with known hypersensitivity or allergy to the drug.

This drug should also be used with caution in animals with preexisting kidney disease.

Since this drug is often considered the only option for animals dying from fatal fungal infections, there are not specific contraindications.

Amphotericin B may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with amphotericin B. Such drugs include tetracycline, digoxin, certain antibiotics and corticosteroids.

Adverse effects of the drug include kidney damage, loss of appetite, vomiting and fever.

Cats seem to be more sensitive to the kidney effects of amphotericin B than dogs.

How Amphotericin B is Supplied

Amphotericin B is available in 50 mg/vial and 100 mg/20 ml vial concentrations.

Dosing Information

Medication should never be administered without first consulting your veterinarian.

For dogs, amphotericin B is administered by two different methods – rapid infusion and slow infusion.

Rapid infusion – Amphotericin B is diluted in 30 ml of 5% dextrose solution. A dose of 0.125 mg per pound (0.25 mg/kg) is given intravenous over 5 minutes. The amphotericin B is then given at a dose of 0.25 mg per pound (0.5 mg/kg) IV three times a week until a total accumulated dose of 5 to 6 mg per pound (9 to 12 mg/kg) is given.

Slow infusion – Amphotericin B is diluted in 250 to 500 ml of 5% dextrose solution. A dose of 0.125 mg per pound (0.25 mg/kg) is given intravenous over 4 to 6 hours. The amphotericin B is then repeated at a dose of 0.25 mg per pound (0.5 mg/kg) intravenous three times weekly until a total accumulated dose of 5 to 6 mg per pound (9 to 12 mg/kg) is given.

Other protocols and doses are available in combination treatment with ketoconazole and flucytosine.

For cats, amphotericin B is diluted in 30 ml of 5% dextrose solution. A dose of 0.125 mg per pound (0.25 mg/kg) is given intravenous. The amphotericin B is then given at a dose of 0.125 mg per pound (0.25 mg/kg) IV three times a week until a total accumulated dose of 5 to 6 mg per pound (9 to 12 mg/kg) is given.

The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.