Itraconazole is a broad-spectrum triazole antifungal agent widely used in veterinary medicine to treat both superficial and systemic fungal infections. In avian medicine, it is one of the primary drugs used to manage aspergillosis, a life-threatening fungal infection caused by Aspergillus species. In dogs and cats, itraconazole treats dermatophytosis (ringworm), blastomycosis, histoplasmosis, and other systemic mycoses. This is a prescription medication requiring veterinary supervision due to its potential for serious side effects and drug interactions.
What Is Itraconazole Used For?
Veterinarians prescribe itraconazole for a wide range of fungal infections:
- Aspergillosis — the most common and dangerous fungal infection in birds, affecting the respiratory system including air sacs and lungs
- Dermatophytosis (ringworm) — fungal skin infections in dogs and cats
- Blastomycosis — systemic fungal infection in dogs, endemic to certain geographic regions
- Histoplasmosis — systemic mycosis common in cats and dogs in endemic areas
- Cryptococcosis — yeast infection particularly common in cats
- Malassezia dermatitis — yeast-related skin and ear infections in dogs
In birds, aspergillosis is often a disease of immunocompromised or stressed individuals. Itraconazole may be used as a sole agent in early or mild cases, or in combination with other antifungals (such as amphotericin B or terbinafine) for severe or disseminated disease.
How Does Itraconazole Work?
Itraconazole inhibits the fungal cytochrome P-450 enzyme lanosterol 14-alpha-demethylase, which is essential for the synthesis of ergosterol — a critical component of the fungal cell membrane. Without ergosterol, the fungal cell membrane becomes unstable and permeable, leading to cell death. Because mammalian and avian cells use cholesterol rather than ergosterol, itraconazole achieves selective toxicity against fungi while sparing host cells, though some cross-reactivity with mammalian cytochrome P-450 enzymes accounts for its side effect profile.
Itraconazole is highly lipophilic and accumulates in keratinized tissues (skin, nails, feathers), making it particularly effective for dermatophytosis. It also achieves good concentrations in lung tissue and respiratory secretions.
Dosage
Dosing must be determined by your veterinarian. Formulation matters — oral solution and capsules are not bioequivalent.
| Species | Typical Dose | Route | Frequency |
|---|---|---|---|
| Birds | 5—10 mg/kg | Oral | Every 12—24 hours |
| Dogs | 5—10 mg/kg | Oral | Every 24 hours |
| Cats | 5—10 mg/kg | Oral | Every 24 hours |
Formulation is critical: The oral solution (Itrafungol/Sporanox liquid) has higher and more predictable bioavailability than capsules. In birds, the liquid formulation is strongly preferred because it can be accurately dosed for small body weights and administered directly into the crop. Compounded formulations should be obtained only from reputable veterinary compounding pharmacies, as itraconazole stability in compounded suspensions varies.
Treatment for aspergillosis in birds is prolonged, often lasting weeks to months. Pulse therapy (alternating periods on and off medication) may be used for dermatophytosis in dogs and cats. Never stop treatment early without veterinary guidance, as fungal infections commonly relapse.
Side Effects
Common side effects include:
- Decreased appetite or anorexia
- Gastrointestinal upset (vomiting, diarrhea)
- Mild lethargy
Serious side effects requiring immediate veterinary attention:
- Hepatotoxicity — liver damage is the most significant concern; signs include jaundice (yellow skin, gums, or sclera), vomiting, dark urine, and severe lethargy
- Skin vasculitis — ulcerative skin lesions, reported primarily in dogs at higher doses
- Congestive heart failure — itraconazole has negative inotropic effects; avoid in patients with heart disease
- Neurological signs — ataxia or limb weakness at high doses
In birds, signs of toxicity may be subtle. Watch for fluffed feathers, reduced droppings, regurgitation, or changes in droppings color (especially yellow or green urates suggesting liver stress).
Drug Interactions
Itraconazole is a potent inhibitor of cytochrome P-450 3A4, leading to numerous significant drug interactions:
- Cisapride — concurrent use is contraindicated due to risk of fatal cardiac arrhythmias
- Cyclosporine, tacrolimus — itraconazole dramatically increases levels of these immunosuppressants
- Midazolam, alprazolam — enhanced sedation
- Calcium channel blockers — increased risk of hypotension
- Antacids, H2 blockers, proton pump inhibitors — reduce itraconazole capsule absorption (less effect on oral solution)
- Warfarin — increased anticoagulant effect
Monitoring
- Baseline liver values (ALT, ALP, bilirubin) before starting treatment
- Repeat liver panels every 2 to 4 weeks during treatment
- In birds, monitoring may include bile acids or plasma protein electrophoresis
- Therapeutic drug monitoring (itraconazole trough levels) can optimize dosing, especially for aspergillosis
Species-Specific Considerations
Birds: Avian aspergillosis carries a guarded prognosis even with treatment. The unique avian respiratory system — with air sacs, pneumatic bones, and a unidirectional airflow pattern — means fungal infection can spread extensively before clinical signs appear. Itraconazole penetrates well into respiratory tissue but may not reach adequate concentrations within dense fungal granulomas. Nebulization therapy with other antifungals is often used concurrently.
Dogs: Pulse therapy (one week on, one week off) is commonly used for dermatophytosis. For systemic mycoses, continuous daily therapy for months is standard.
Cats: The Itrafungol oral solution is approved for cats in many regions and is the preferred formulation. Cats generally tolerate itraconazole well, though liver monitoring is still essential.
Storage
Store at room temperature, protected from light and moisture. Do not freeze the oral solution.
Always consult your veterinarian before starting, stopping, or changing any medication. This information is for educational purposes and does not replace professional veterinary advice.