What is Itraconazole? — How to Safely Use This Antifungal for Dogs and Cats

Skin & CoatQ&AMeongsiljang Veterinary Advisory Board

Itraconazole is the most commonly used oral antifungal for treating fungal skin infections and systemic fungal infections in dogs and cats. We’ve put together a clear, easy-to-understand guide on how to give it, possible side effects, and important precautions for pet parents.

What is Itraconazole?

A veterinarian preparing itraconazole capsules along with pet food

Itraconazole is an oral antifungal medication used to treat fungal skin diseases and systemic fungal infections in dogs and cats. It is most important to administer it with food. The capsule formulation must be given with meals to ensure proper absorption; giving it on an empty stomach reduces absorption and may diminish therapeutic efficacy. It is considered a first-line treatment option, particularly for cats and small-breed dogs, in cases of dermatophytosis (ringworm), Malassezia infections, and systemic mycoses (such as those caused by Blastomyces and Histoplasma).

What Conditions Is It Used For?

Itraconazole is widely used to treat a variety of fungal infections. Common indications include dermatophytosis (ringworm) of the skin, recurrent Malassezia infections of the ears and skin, and systemic mycoses involving fungal invasion of the lungs (such as Aspergillus, Histoplasma, Blastomyces, and Cryptococcus). In particular, itraconazole is recommended as the first-line treatment for Microsporum canis infections in cats.

Comparison with Other Antifungals

Item	Itraconazole	Fluconazole	Ketoconazole
Absorption conditions	With food	Can be taken on an empty stomach	With food
Liver burden	Moderate	Low	High
Dermatophytosis	First-line choice	Low efficacy (not recommended)	Can be used
Systemic mycosis	First-line choice	Effective (depending on disease)	Rarely used
Safety in cats	Recommended (regular testing)	Safe	Caution

Based on veterinary dermatology and internal medicine textbooks. Fluconazole is less effective against dermatophytes but is effective against systemic mycoses such as blastomycosis and histoplasmosis. The final choice is made by the veterinarian depending on the disease and the patient's condition.

Proper Administration Method

It’s essential to administer itraconazole with food, especially a diet containing fat. The capsule formulation is better absorbed in the acidic environment of the stomach, so its effectiveness may be reduced if taken concurrently with acid-suppressing medications like omeprazole, which raise gastric pH. The commercially available liquid formulation for cats (Itrafungol) generally has better absorption than capsules. However, compounded formulations prepared at pharmacies are not recommended due to studies showing lower bioavailability. Dosage should be determined by your veterinarian based on your pet’s weight and the specific condition being treated; never reduce or skip doses without veterinary guidance.

Liquid itraconazole for cats to be administered with food

Contact Your Vet Immediately If This Happens

If your pet develops a loss of appetite, vomiting, diarrhea, or lethargy while taking itraconazole, it could be a sign of liver toxicity. Jaundice, indicated by yellowing of the gums or the whites of the eyes, is a medical emergency. Although rare, ulcerative skin rashes have also been reported; in such cases, stop administering the medication immediately and consult your veterinarian.

Side Effects and Liver Enzyme Monitoring

According to veterinary pharmacology and internal medicine textbooks, common side effects of itraconazole include loss of appetite, vomiting, diarrhea, and elevated liver enzymes (such as ALT). When using azole antifungals, particularly itraconazole, in cats, it is recommended to check liver values once within 2–4 weeks after starting treatment, followed by regular monthly monitoring. Renal (proximal tubular) changes have also been reported in cats, so kidney values should be checked periodically as well. If there is a significant rise in these values or if clinical signs develop, the dosage should be reduced or the medication discontinued. Regular blood tests are especially important in cases of systemic mycosis, which often require prolonged treatment.

A veterinary technician drawing blood from a dog for liver function tests

Medications to Avoid Taking Together

Itraconazole can affect the cytochrome P450 enzyme system in the liver, which may lead to interactions with other medications. - Acid-suppressing drugs: Medications that raise stomach pH, such as omeprazole and famotidine, can interfere with absorption. - Immunosuppressants (cyclosporine): Because itraconazole inhibits P450 metabolism, blood levels of cyclosporine may rise, potentially requiring dosage adjustments. - Other drugs metabolized by P450: Co-administration may alter the blood concentrations of either drug, possibly necessitating dosage adjustments. - Compromised cardiac function: Itraconazole may have a negative inotropic effect (reducing the heart's contractile force), so caution is advised. Be sure to inform your veterinarian of any medications your pet is currently taking.

If Your Pet Is Pregnant or Has Heart or Liver Disease

Itraconazole is generally avoided in pregnant pets due to the risk of birth defects. It should also be used with caution in animals with a history of congestive heart failure, as it may worsen symptoms. If your pet has pre-existing liver disease, dosage adjustments may be necessary, so it’s essential to check liver function through blood tests before starting treatment.

Treatment Duration and Preventing Recurrence

Treatment for dermatophytosis and Malassezia infections typically lasts several weeks, but the guiding principle is to continue therapy until mycological cure is confirmed through methods such as fungal culture, even if this extends beyond the initial planned duration. To prevent relapse, medication should be continued for a specified period (e.g., several additional weeks) after clinical symptoms have resolved. Systemic fungal infections generally require prolonged treatment for several months (e.g., 4–6 months) or longer, with therapy continuing for an additional 4–6 weeks after clinical cure. Stopping treatment prematurely once symptoms disappear carries a high risk of relapse; for instance, relapse rates of approximately 20–25% have been reported in dogs with blastomycosis. Concurrent environmental disinfection, including washing bedding, toys, and food bowls, is essential to prevent reinfection.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

I missed one dose of itraconazole. What should I do?

You can give it with your pet’s meal as soon as you remember. If it’s close to the next scheduled dose, skip the missed one and resume the regular schedule. Never give two doses at once.

Can I crush human medication and give it to my pet?

Crushing the capsule may alter its absorption rate. For safety, use liquid formulations designed for pets or medications prepared according to your veterinarian’s prescribed dosage.

When will the effects start to appear?

Skin symptoms typically begin to improve after 2–3 weeks. Systemic fungal infections are confirmed via imaging tests 1–2 months later. Even if visible improvement is slow, do not discontinue treatment on your own.

Is it more dangerous for cats?

Cats have different liver metabolism, so they are more prone to loss of appetite and weight loss. That’s why a liquid formulation specifically for cats has been developed, and regular blood tests are especially important.

Can I give this supplement alongside other supplements?

Omega-3 and probiotics are generally fine. However, calcium supplements or gastrointestinal medications with antacid effects may interfere with absorption, so please consult your veterinarian.

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References

[1] Canine and Feline Respiratory Medicine, 3rd Edition - Antifungal Therapy

[2] BSAVA Manual of Canine and Feline Dermatology, 4th Ed - Malassezia and Dermatophytosis

[3] Small Animal Critical Care Medicine, 3rd Ed - Antifungal Drugs

[4] Clinical Medicine of the Dog and Cat, 4th Ed - Systemic Mycoses

[5] Vlaminck K, Engelen M (2005) Pharmacokinetic studies of itraconazole for feline Microsporum canis dermatophytosis, Advances in Veterinary Dermatology 5, 130-136