Itraconazole Side Effects in Cats: What to Watch For

Name: Itraconazole Side Effects in Cats: What to Watch For
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

Itraconazole for cats side effects most often involve the stomach and intestines, with vomiting and appetite loss being the problems owners notice first. Liver changes can also happen, which is why veterinarians check blood work before and during treatment. Most cats finish a course of itraconazole safely when the dose is right and monitoring is in place.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

Vomiting, appetite loss, and diarrhea are the most common reasons owners call the clinic during itraconazole treatment.
Liver enzyme changes can develop without obvious signs, so blood work before and during treatment matters more than how your cat looks.
Give the medicine with food unless your veterinarian says otherwise, since food improves absorption and can ease stomach upset.
Never adjust the dose on your own. Your veterinarian calculates it from your cat's weight and health status.
Call your veterinarian the same day if your cat stops eating, vomits repeatedly, or turns yellow around the gums, eyes, or ears.

What Itraconazole Is and What Veterinarians Use It For

Itraconazole is an oral antifungal drug. In cats, veterinarians prescribe it most often for fungal skin and mucosal infections, including sporotrichosis, a fungal disease that cats can pass to people through scratches and bites. Itraconazole is considered the first-line treatment for feline sporotrichosis [1].

Treatment can be long. In one study of 29 cats with cutaneous and mucosal sporotrichosis, clinical cure took a median of 10 weeks of treatment [1]. Some cats need months of therapy, and the length depends on the infection, how deep it goes, and how well your cat responds.

Itraconazole is also used for other fungal conditions in cats, such as ringworm that has not responded to other treatments. Your veterinarian will confirm the diagnosis before prescribing, usually with a fungal culture, cytology, or other testing.

How Itraconazole Works

Itraconazole attacks the fungal cell membrane. Fungi need a compound called ergosterol to keep that membrane stable, and itraconazole blocks the step where the fungus builds it. Without a stable membrane, the fungus cannot grow and spread normally, and the cat's immune system can clear it.

This is why the drug works slowly. It does not kill every fungus cell at once. It weakens the infection over weeks while the body does the rest of the work. That slow pace is also why stopping treatment early often leads to relapse.

Because itraconazole is processed mainly by the liver, liver function matters during treatment. It can also affect the balance of bacteria in the gut. In a study of 16 healthy cats given itraconazole at 5 mg/kg/day orally with food, bacterial populations stayed stable during treatment, but some measures of bacterial diversity dropped after treatment ended [2]. Researchers are still working out what that means for everyday patients.

Dosing Basics for Cats

Your veterinarian decides the dose. It is calculated from your cat's weight, the specific infection, and your cat's liver status. Do not use a dose from the internet, a friend's cat, or an old bottle.

Itraconazole comes as a liquid solution and as capsules. The solution is often given with food because food improves absorption. In the microbiome study described above, healthy cats received 5 mg/kg/day of the solution orally with food [2]. That is a research dose, not a prescription for your cat. Your veterinarian will set your cat's actual dose.

A few practical points:

Give the medicine at the same time each day, with a meal if your veterinarian recommends it.
If your cat vomits right after the dose, do not give a second dose without asking your veterinarian first.
If you miss a dose, give it when you remember unless it is almost time for the next one. Then skip the missed dose and go back to the normal schedule. Never double up.
Keep the bottle or capsules out of reach of pets and children.
Wash your hands after giving the medicine, especially if you are pregnant, immunocompromised, or caring for someone who is.

If your cat is hard to medicate, ask your veterinarian about flavored liquids, pill pockets, or compounding. Do not crush or split capsules unless your veterinarian or pharmacist confirms it is safe for that specific product.

Itraconazole for Cats Side Effects: What to Watch For

Most side effects are manageable when they are caught early. The table below covers what owners report and what to do about each one.

Side effect	How common or serious	What to do
Vomiting	Common, usually mild	Give with food. If vomiting repeats or your cat cannot keep food down, call your veterinarian the same day.
Appetite loss	Common	Offer small, warm, smelly meals. If your cat refuses food for more than 24 hours, call your veterinarian.
Diarrhea	Common, usually mild	Keep water available. Call if diarrhea is bloody, frequent, or lasts more than a day or two.
Lethargy	Less common	A quiet day can be normal. Persistent weakness or collapse needs same-day care.
Liver enzyme changes	Detected on blood work, often with no visible signs	Keep every recheck appointment. Report yellow gums, eyes, or skin right away.
Skin reactions	Uncommon	Rash, hives, or facial swelling need prompt veterinary attention.
Jaundice (yellow gums, eyes, ears)	Rare but serious	Emergency. Call your veterinarian or an emergency clinic immediately.

Adverse drug reactions were reported in 2 of 29 cats (6.9%) in the sporotrichosis study, and no deaths occurred during that study [1]. That is reassuring, but it does not mean side effects are rare in every situation. Cats with liver disease, cats on other medications, and cats on higher doses face more risk.

Vomiting and Stomach Upset

Vomiting is the side effect owners mention most. It often improves when the medicine is given with a full meal instead of an empty stomach. If your cat vomits once and seems fine, note it and continue as directed. If your cat vomits repeatedly, vomits blood, or seems painful in the belly, stop and call your veterinarian.

Appetite Loss

A cat that stops eating is a cat in trouble. Appetite loss can come from nausea, from the infection itself, or from liver changes. Try warming the food slightly and offering small portions more often. If your cat has not eaten in 24 hours, or has stopped drinking, call your veterinarian. Cats who go without food for several days can develop serious liver problems.

Liver Changes

Itraconazole is metabolized by the liver, so veterinarians typically check liver values before starting treatment and again during treatment. Many cats have mild enzyme increases with no signs at all. These often improve when the dose is lowered or the drug is stopped. Yellow gums, yellow skin, dark urine, or sudden lethargy point to a bigger problem and need immediate care.

Skin Reactions

Skin reactions are uncommon but possible with almost any drug. Watch for hives, swelling around the face or muzzle, or a rash that spreads. Facial swelling or trouble breathing is an emergency.

If your cat takes other medications, side effect patterns can overlap. Our guide to cat allergy medication side effects explains how to sort out which drug is causing which sign. If your cat also takes gabapentin for pain or anxiety, sedation and appetite changes can have more than one cause.

Who Should Not Take Itraconazole

Itraconazole is not right for every cat. Your veterinarian will weigh the risks if your cat:

Has liver disease or abnormal liver values
Is pregnant or nursing
Is very young or underweight
Has heart disease, since itraconazole can affect heart muscle function in some patients
Takes other drugs that interact with it

Drug interactions matter. Itraconazole can raise or lower blood levels of other medications, and some medications raise itraconazole levels in ways that increase side effects. Tell your veterinarian about everything your cat takes, including flea and tick products, dewormers, heart medications, seizure medications, steroids, and supplements. If your cat takes seizure medication, our article on seizure medication side effects in cats covers what to watch for when drugs are combined.

Some fungal infections do not respond to itraconazole alone. In a study from Thailand, 687 of 1,178 feline Sporothrix isolates showed reduced susceptibility to itraconazole [3]. In another case, a cat with an itraconazole-resistant eye infection improved only after treatment was changed to terbinafine plus high-dose itraconazole, and the eyelid healed after 5 months of antifungal therapy [4]. Treatment failure does not always mean the drug is weak. A study at the Brazil border found that treatment failures were not caused by elevated itraconazole MICs before treatment started [5]. Your veterinarian may recommend susceptibility testing or a different drug combination if your cat is not improving.

Overdose and When to Call for Help

If your cat eats extra doses or chews through a container, call for help right away. Do not wait for signs to appear.

Pet Poison Helpline: (855) 764-7661
ASPCA Animal Poison Control Center: (888) 426-4435

Have the product name, the strength, the amount your cat may have swallowed, and your cat's weight ready. A veterinary poison control specialist can tell you whether your cat needs to be seen and what treatment is needed. Signs of overdose can include severe vomiting, drooling, tremors, weakness, and collapse.

If your cat has any of these signs after a normal dose, treat it as an emergency too.

Limitations and When to Contact a Veterinarian

No article can tell you what is happening with your cat. Your veterinarian knows your cat's history, blood work, and infection, and that context decides what is safe.

Call your veterinarian the same day if your cat:

Vomits more than once or cannot keep food down
Refuses food for more than 24 hours
Has diarrhea that is bloody or lasts more than a day or two
Seems weak, wobbly, or much quieter than usual
Develops a rash, hives, or swelling

Go to an emergency clinic now if your cat:

Has yellow gums, eyes, or skin
Collapses, has a seizure, or has trouble breathing
Has facial swelling or hives with breathing changes
Vomits blood or has black, tarry stool

Keep every recheck appointment, even when your cat looks well. Blood work catches liver changes before you can see them. If cost is a concern, ask your veterinarian which tests are most important and whether a payment plan is available.

Frequently Asked Questions

How long do itraconazole side effects last in cats?

Most mild stomach signs ease within a few days once the medicine is given with food or the dose is adjusted. Liver changes take longer to normalize and are tracked with repeat blood work. If a sign lasts more than a day or two, call your veterinarian instead of waiting it out.

Can I stop itraconazole if my cat seems better?

No. Stopping early is one of the main reasons fungal infections come back. Cats often look normal before the infection is fully cleared, and treatment usually continues for weeks after the skin or lesions look healed. Only your veterinarian should decide when to stop.

Does itraconazole cause liver failure in cats?

Serious liver injury is uncommon, but mild liver enzyme increases are a known risk, which is why blood work is checked during treatment. Yellow gums, yellow skin, or sudden collapse are warning signs that need emergency care. Most cats recover when the drug is stopped early.

Should I give itraconazole with food?

Yes, in most cases. Giving the solution with food improves absorption and can reduce nausea. Your veterinarian will tell you the exact schedule for your cat's product, since capsules and liquids are not handled the same way.

Can my other pets or I catch the infection my cat is being treated for?

Some fungal infections in cats, including sporotrichosis, can spread to people and other animals through scratches, bites, or contact with drainage from wounds [1]. Wear gloves when handling wounds or applying medication, wash your hands afterward, and ask your veterinarian about household precautions. People who are pregnant or immunocompromised should take extra care.

References

Prospective Uncontrolled Interventional Study of Itraconazole and β-Glucans (Euglena gracilis) to Assess Safeness and Clinical Effectiveness in Cats with Cutaneous and Mucosal Sporotrichosis. Veterinary sciences, 2025.
Oral itraconazole may alter the gastrointestinal microbiome in healthy cats. American journal of veterinary research, 2026.
In Vitro Antifungal Drug Susceptibility of Feline Sporothrix schenckii Complex Isolates, Thailand, 2023-2025. Emerging infectious diseases, 2026.
Successful treatment of localised ocular sporotrichosis caused by itraconazole-resistant Sporothrix schenckii complex in a cat. JFMS open reports, 2026.
Sporothrix brasiliensis Treatment Failure without Initial Elevated Itraconazole MICs in Felids at Border of Brazil. Emerging infectious diseases, 2025.