Ketoconazole (Nizoral®)

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Ketoconazole (Nizoral®)

By: Dr. Mark Papich

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Overview

Ketoconazole belongs to a general class of drugs known as antifungal drugs. Other related drugs in this class include itraconazole, miconazole and fluconazole.

Ketoconazole inhibits the growth of fungal organisms by interfering with the formation of the fungal cell wall.

Ketoconazole is effective only against fungal or yeast organisms. These fungi are the ones that cause skin infections (dermatophytes) commonly known as "ringworm" and toenail infections. However, the drug is also effective for some of the more serious fungal infections, such as blastomycosis, coccidoidomycosis and cryptococcosis. These infections can affect the skin, lymph nodes, eyes, bone and respiratory tract (lungs).

Ketoconazole 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: Nizoral® (Janssen) and various topical formulations

Veterinary formulations: None

Uses of Ketoconazole

Ketoconazole is used in both dogs and cats to treat infections caused by fungi. These infections may affect the skin, claws, lymph nodes, respiratory tract, bone and other tissues.

Infections treated by ketoconazole include blastomycosis, histoplasmosis, yeast infections (Malassezia) and dermatophyte infections (dogs and cats).

Ketoconazole is not effective against infections caused by bacteria, parasites (intestinal worms), mites, or viruses.

Ketoconazole suppresses hormone synthesis and has been used in rare instances to treat conditions associated with excessive production of the hormone cortisone from the adrenal gland (Cushing's Disease).

Precautions and Side Effects

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

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

Ketoconazole may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with ketoconazole. Such drugs include antacids, cimetidine, cisapride, methylprednisolone, anticonvulsants, heart medications, cyclosporine and theophylline.

The most serious adverse effect is that which affects the liver (hepatitis). Signs of decreased appetite, jaundice, vomiting or diarrhea should be reported to your veterinarian.

Ketoconazole may cause vomiting, diarrhea and decreased appetite.

Ketoconazole has caused changes in the hair coat of animals, causing a lightening of the hair color in dogs and a drying of the hair coat in cats.

Eye problems (cataracts) have been associated with administration of ketoconazole in dogs.

Ketoconazole inhibits the hormone synthesis in animals and treated animals have decreased levels of cortisol (cortisone), testosterone and other sex hormones. These changes may affect reproduction and cause some animals to appear depressed or lethargic.

Do not administer ketoconazole to a pregnant animal because it has caused fetal death.

How Ketoconazole Is Supplied

Ketoconazole is available as a 200 mg tablet.

Dosing Information

Medication should never be administered without first consulting your veterinarian.

The usual dose for dogs is 5 to 7 mg per pound (10 to 15 mg/kg) every 12 hours orally.

The dose for cats is 2.5 to 5 mg per pound (5 to 10 mg/kg) every 12 hours orally. For yeast infections of the skin (Malassezia) the dose is 2.5 mg per pound (5 mg/kg) per day orally.

It is common for fungal infections to require several weeks of treatment.

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.