Ketoconazole Uses for Dogs

Fungal infections in dogs can manifest in various ways, affecting both the skin and internal organs. Subcutaneous and systemic mycoses typically present as nodules, ulcerated plaques, or circular, crusted, and alopecic lesions that may exude serous, purulent, or hemorrhagic fluid. Antifungal medications are crucial in treating these integumentary diseases.

Understanding Antifungal Medications

Several antifungal drugs are available for veterinary use, each with its own spectrum of activity, potency, and potential side effects. Among these are itraconazole, ketoconazole, fluconazole, terbinafine, griseofulvin, amphotericin B, and flucytosine. Systemic iodides are also used for specific fungal infections.

Itraconazole

Itraconazole is a synthetic, broad-spectrum antifungal belonging to the imidazole family. It works by inhibiting ergosterol synthesis, a key component of fungal cell membranes, leading to cell wall rupture. Itraconazole is effective against a wide range of fungi, including dermatophytes, Malassezia, Candida, Cryptococcus, Histoplasma, Blastomyces, and Sporothrix spp., as well as certain protozoans.

Dosages for dogs include 5 mg/kg PO every 24 hours for dermatophytosis until mycological cure, and 5-10 mg/kg PO every 24 hours for 60 days for systemic mycoses. A severe, dose-related ulcerative dermatitis can occur in 5%-10% of dogs receiving doses greater than 10 mg/kg. Early identification and drug withdrawal are crucial for resolution.

Ketoconazole

Ketoconazole, an imidazole antifungal, was one of the first medications used to treat localized or systemic fungal infections in dogs. While it shares a similar antifungal mechanism with itraconazole, ketoconazole has lower potency, increased toxicity, and a narrower spectrum of activity. For serious systemic diseases, it is often used in combination with amphotericin B due to its delayed therapeutic effect.

Efficacy and Uses of Ketoconazole

Ketoconazole is active against various fungal pathogens:

• Dermatophytosis: Effective against Trichophyton verrucosum, T. equinum, T. mentagrophytes, Microsporum canis, and M. nanum at a dosage of 10 mg/kg PO every 24 hours for 4-8 weeks.
• Yeast Infections: Active against Malassezia pachydermatis (10 mg/kg PO every 24 hours for 3 weeks) and Cryptococcus neoformans (10 mg/kg PO every 24 hours for 6-18 months).
• Candidiasis: The dosage is 10 mg/kg PO every 24 hours for 6-8 weeks, with a maintenance dose of 2.5-5 mg/kg in chronic cases.
• Systemic Mycoses: Coccidioidomycosis often responds better to ketoconazole than amphotericin B, with a minimal treatment period of 12 months for disseminated disease. Blastomycosis, histoplasmosis, and cryptococcosis may be treated with a combination of ketoconazole and amphotericin B, which can reduce nephrotoxic signs compared to amphotericin B alone.

For blastomycosis, a combination of amphotericin B (4-6 mg/kg total dose) with ketoconazole (20 mg/kg PO every 24 hours for 60-90 days in dogs, and 10 mg/kg PO every 24 hours for 60-90 days in cats) is used. For histoplasmosis, amphotericin B (2-4 mg/kg total dose) is combined with ketoconazole (20 mg/kg PO every 24 hours for 4-6 months in dogs, and 10 mg/kg PO every 24 hours for 9-12 months in cats).

Ketoconazole and Cushing's Disease

Ketoconazole inhibits cortisol synthesis and has been used to treat canine pituitary-dependent hyperadrenocorticism (Cushing's Disease) at 10 mg/kg PO every 24 hours. If cortisol levels remain high after 10 days, the dosage may be increased to 15 mg/kg PO every 24 hours. Studies have shown that ketoconazole can reduce corticosteroid levels in dogs with hyperadrenocorticism.

Absorption and Administration

Ketoconazole requires an acidic environment for optimal absorption. Therefore, doses should be administered with food to stimulate hydrochloric acid production in the stomach. Concurrent administration of H2-blockers or antacids is contraindicated as they reduce stomach acidity.

Cost of Treatment

The cost of treating a medium-sized dog (approximately 45 pounds) with oral ketoconazole is about $0.50 per day at a typical dose. Topical creams and shampoos average $15 per container.

Dosage and Duration

The usual dose for most acute fungal and yeast infections in dogs is 10 mg/kg by mouth, twice daily. Treatment duration typically ranges from six to eight weeks. For chronic infections, a maintenance dose of 2.5 to 5 mg/kg once daily may be used. The dose is adjusted in dogs with liver or kidney function issues.

Side Effects of Ketoconazole

Common adverse effects in dogs include decreased appetite, weight loss, nausea, vomiting, diarrhea, hair loss, itchy skin, temporary infertility in males, changes in hair color, reduced blood platelet count, cataracts (with long-term use), birth defects, and liver toxicity. Cats appear to be more sensitive, and some clinicians avoid its use in this species due to risks of anorexia, fever, depression, diarrhea, and increased liver enzymes.

Drug Interactions

Ketoconazole can interact with a wide range of medications, including alcohol, antacids, antiarrhythmics, tricyclic antidepressants, benzodiazepines, anti-anxiety medications, certain antibiotics, chemotherapy drugs, corticosteroids, narcotics, and blood thinners. It is essential to inform your veterinarian about all medications, supplements, or vitamins your dog is taking.

Considerations and Monitoring

Ketoconazole should be used with caution in pregnant or nursing females, dogs with liver disease, or those who are severely ill or have undergone surgery or trauma. Regular blood tests for liver enzymes and platelet counts are recommended during treatment. Liver enzymes and platelet count blood tests should be performed every 2-3 months to detect adverse effects.

Allergic Reactions and Sensitivity

As with any medication, there is a risk of allergic reactions or sensitivity to ketoconazole. Symptoms such as swelling, itching, or hives warrant immediate veterinary attention.

Storage and Missed Doses

Ketoconazole should be stored in a cool, dry place. If a dose is missed, administer it as soon as remembered, unless it is nearly time for the next scheduled dose. Do not double up doses. In case of accidental overdose, contact your veterinarian or an emergency veterinary clinic immediately.

Other Antifungal Medications

Fluconazole

Fluconazole is a fungistatic triazole compound similar in action to ketoconazole but does not affect mammalian hormone synthesis. It is particularly useful for treating CNS mycoses due to its molecular size and low protein binding. It is primarily used for systemic mycoses like Cryptococcus, Histoplasma, and Blastomyces spp. The dosage for dogs is 2.5-10 mg/kg PO every 24 hours for 56-64 days. Fluconazole does not require a low pH for absorption and can be given with or without food.

Terbinafine

Terbinafine is an allylamine that interferes with fungal sterol biosynthesis. It concentrates in hair follicles and sebum-rich skin. The dosage in cats is 10-30 mg/kg PO every 24 hours until mycological cure. In dogs, it is well absorbed but does not accumulate in the skin as it does in cats. Rare cases of hepatic toxicity and gastrointestinal signs can occur in humans.

Griseofulvin

Griseofulvin is effective only against dermatophytes. Its absorption can be enhanced by administration with a fat-containing meal. It concentrates in the skin, hair, and nails. Adverse effects in dogs include vomiting, diarrhea, and increased liver enzyme activity. In cats, anemia, leukopenia, vomiting, diarrhea, depression, pruritus, fever, and ataxia have been noted. Bone marrow suppression can occur, especially in FIV-positive cats and kittens.

Amphotericin B

Amphotericin B is a polyene antifungal administered parenterally. It is used for progressive or disseminated deep mycosis and can be combined with other agents. It is administered intravenously, often diluted in 5% glucose, over 2-6 hours. The dosage is 0.15-0.5 mg/kg every 48 hours until a cumulative dose of 4-12 mg/kg is reached. The major adverse effect is nephrotoxicity, with cats being more sensitive. Pre-medication can help reduce adverse effects like fever, nausea, and vomiting.

Flucytosine

Flucytosine is a fluorinated pyrimidine effective against Cryptococcus neoformans and Candida. Resistance develops frequently, so it is often combined with amphotericin B. The dosage in dogs and cats is 25-50 mg/kg PO every 6-8 hours for 42 days. Adverse effects include gastrointestinal disturbances and bone marrow suppression.

Systemic Iodides

Systemic iodides are used for specific fungal infections like sporotrichosis. Dogs are treated with potassium iodide (40 mg/kg PO every 12 hours for 60 days). Adverse effects in small animals include vomiting, diarrhea, depression, and inappetence. Systemic iodide may also cause abortion and should not be used in pregnant or lactating animals.

tags: #what #is #ketoconazole #for #dogs