Ketoconazole

Drug Class: Antifungal | Pharmacological Group: Azole antifungal (imidazole)

Mechanism of Action: Ketoconazole inhibits the synthesis of ergosterol, a vital component of the fungal cell membrane, by blocking the cytochrome P450 enzyme lanosterol 14α-demethylase. This leads to increased membrane permeability and leakage of cellular contents, ultimately causing fungal cell death. It is primarily fungistatic but may be fungicidal at high concentrations. It also inhibits fungal cytochrome P450 enzymes, which can affect the metabolism of other drugs.

Pharmacodynamics: Ketoconazole exhibits a broad spectrum of antifungal activity against dermatophytes (e.g., Microsporum, Trichophyton), yeasts (e.g., Malassezia, Candida), and some dimorphic fungi (e.g., Blastomyces, Histoplasma). It is less effective against Aspergillus and Mucor species. In addition to antifungal effects, ketoconazole inhibits mammalian cytochrome P450 enzymes, particularly CYP3A4, leading to significant drug interactions. It also inhibits steroidogenesis, reducing cortisol and testosterone synthesis, which can be exploited therapeutically in conditions like hyperadrenocorticism.

Common:

• Anorexia
• Vomiting
• Diarrhea
• Lethargy
• Elevated liver enzymes (ALT, AST, ALP)

Serious / Severe:

• Hepatotoxicity (especially in cats)
• Adrenal suppression (cortisol deficiency)
• Thrombocytopenia
• Leukopenia
• Hemolytic anemia
• QT prolongation (rare)
• Teratogenicity (in pregnant animals)

Rare:

• Cutaneous reactions (erythema, pruritus)
• Photosensitivity
• Neurotoxicity (ataxia, seizures)
• Gynecomastia (due to antiandrogenic effects)
• Alopecia

Signs of Toxicity:

• Severe vomiting
• Diarrhea
• Anorexia
• Lethargy
• Hepatotoxicity (elevated liver enzymes, jaundice)
• Adrenal insufficiency (weakness, collapse, electrolyte imbalances)
• Respiratory depression (rare)

Emergency Treatment Protocol: Treatment is primarily supportive. Induce emesis if ingestion is recent (within 1-2 hours) and the animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids for dehydration and electrolyte imbalances. Monitor liver enzymes and adrenal function. In severe cases, consider administration of glucocorticoids (e.g., prednisolone) for adrenal suppression. There is no specific antidote; symptomatic and supportive care is essential.

Withdrawal times are not established for ketoconazole in food animals. The values provided are conservative estimates based on pharmacokinetic data and are intended for extra-label use under veterinary supervision. For cattle, a meat withdrawal of at least 7 days and milk withdrawal of 3 days is suggested. For poultry, egg withdrawal is not applicable as ketoconazole is not commonly used in laying hens. Always consult the label or a veterinary pharmacologist for specific withdrawal recommendations.

Storage Temperature: Store at controlled room temperature, 20-25°C (68-77°F). Protect from moisture.

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Keep container tightly closed. Protect from light. Do not freeze oral suspension. Store topical formulations away from excessive heat.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Ketoconazole is FDA-approved for human use; however, there are no FDA-approved veterinary formulations. Veterinary use is extra-label, relying on human-approved products.

Extra-Label (Off-Label) Use: In the United States, ketoconazole is not FDA-approved for veterinary use in food animals. Extra-label use in food animals is permitted under AMDUCA (Animal Medicinal Drug Use Clarification Act) only with a valid veterinarian-client-patient relationship and requires an extended withdrawal period. For companion animals, extra-label use is common and accepted. In the EU, similar regulations apply under Regulation (EC) No 470/2009.