Itraconazole Side Effects in Dogs: What to Watch
By Dr. Zubair Khalid, DVM, MS, PhD ·
Itraconazole for dogs side effects most often show up as vomiting, appetite loss, and changes in liver enzyme values on blood work. Many dogs have mild or no problems, but some develop signs serious enough to stop treatment. Your veterinarian decides whether a symptom is expected or a reason to change the plan.
This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- The most common problems are stomach upset, vomiting, diarrhea, and not wanting to eat.
- Liver enzyme changes are a known concern, which is why veterinarians check blood work before and during treatment.
- Stop the drug and call your veterinarian the same day if your dog vomits repeatedly, refuses food for more than a day, or seems weak or yellow-tinged.
- Never change the dose on your own. Serum drug levels vary widely between dogs, and two dogs on the same dose can have very different blood concentrations [1].
- Keep every recheck appointment. Dose adjustments are common and often happen more than once during treatment [1].
What Itraconazole Is and What Veterinarians Use It For
Itraconazole is an oral antifungal medication. Veterinarians prescribe it to treat serious fungal infections in dogs, including blastomycosis, a fungal disease that can affect the lungs, skin, eyes, and other organs [1].
It is also used in the treatment of some other deep fungal and algal infections. In one report, a dog with a Prototheca infection received itraconazole along with other antifungal drugs as part of a longer treatment plan [2]. In another report, oral itraconazole was part of the treatment approach for dogs with ocular protothecosis, a rare infection that caused blindness in all eight dogs described [3].
These are uncommon diseases. If your dog has been prescribed itraconazole, it usually means your veterinarian has diagnosed or strongly suspects a serious fungal infection that needs long-term treatment.
How Itraconazole Works
Itraconazole works by interfering with the fungal cell membrane. Fungal cells need a compound called ergosterol to keep their membranes stable. Itraconazole blocks a step in making ergosterol, which weakens the fungal cell and slows or stops its growth.
This is why treatment takes months, not days. The drug does not kill every fungal cell at once. It holds the infection back while the dog's immune system clears what remains. In one study of dogs with blastomycosis, the median treatment time was 7.9 months [1]. Your veterinarian will set the length of treatment for your dog based on the infection and how your dog responds.
Dosing Basics: Who Decides, How to Give It, and Missed Doses
Who decides the dose
Your veterinarian calculates the dose from your dog's weight and health. In one study, the starting dose was 5 mg/kg per day, and doses were then adjusted based on blood levels [1]. That number is not a dosing recommendation for your dog. It comes from a research protocol, and your veterinarian will choose the starting dose and any changes.
Why blood levels matter
Itraconazole blood concentrations vary widely between individual dogs. In one study, 12 of 14 dogs needed at least one dose adjustment, and 9 dogs needed more adjustments even after reaching the target range [1]. Researchers also found no clear link between the dose given and the resulting blood concentration [1][4]. This is why some veterinarians monitor drug levels instead of relying on dose alone.
How to give it
Give itraconazole with food unless your veterinarian says otherwise. Food improves absorption for many dogs. If your dog vomits right after a dose, do not give a second dose on your own. Call your veterinarian for instructions.
Missed doses
If you miss a dose, give it when you remember, unless it is almost time for the next one. In that case, skip the missed dose and go back to your regular schedule. Do not double up. If you miss doses often, tell your veterinarian, because gaps in treatment can affect how well the infection is controlled.
Common and Serious Side Effects of Itraconazole for Dogs
| Side effect | How common or serious | What to do |
|---|---|---|
| Vomiting | Common, usually mild | Give with food. If vomiting repeats or your dog cannot keep water down, stop the drug and call your vet the same day. |
| Appetite loss | Common | Offer small, tempting meals. If your dog refuses food for more than 24 hours, stop the drug and call your vet. |
| Diarrhea | Common, usually mild | Watch for blood, black stool, or worsening. Call your vet if it lasts more than a day or your dog seems sick. |
| Lethargy or weakness | Less common, can be serious | Stop the drug and call your vet the same day. |
| Liver enzyme changes | Detected on blood work, often without symptoms | Keep all recheck appointments. Report yellow gums, eyes, or skin right away. |
| Yellowing of gums, eyes, or skin (jaundice) | Serious | Stop the drug and seek veterinary care immediately. |
| Bleeding or bruising easily | Uncommon, serious | Stop the drug and call your vet or an emergency clinic right away. |
| Swelling of the face, hives, trouble breathing | Rare, emergency | Stop the drug and go to an emergency clinic now. |
Stomach upset is the side effect owners notice most. It often improves when the drug is given with a full meal, but repeated vomiting is not something to wait out.
Liver enzyme changes are a known concern with this drug. Your veterinarian will likely check blood work before treatment and at intervals during treatment. Mild rises may not cause any visible signs, and your veterinarian may simply monitor them. Larger rises, or any sign of jaundice, need prompt attention.
Some side effects overlap with problems seen with other long-term medications. If your dog takes other drugs, it helps to know what to watch for. Our guide to antibiotic side effects in dogs covers similar stomach and appetite issues, and our article on thyroid medication side effects explains how long-term drugs can affect behavior and energy.
Who Should Not Take Itraconazole and What Interacts With It
Itraconazole is not right for every dog. Your veterinarian will weigh your dog's liver health, other medications, and overall condition before prescribing it.
Dogs with existing liver disease need extra caution. The liver processes this drug, and dogs with reduced liver function may build up higher drug levels. Blood work before treatment helps your veterinarian decide whether the drug is safe to start.
Pregnancy and breeding status matter. If your dog is pregnant, nursing, or intended for breeding, tell your veterinarian before starting treatment.
Drug interactions are a real concern. Itraconazole affects how the body handles many other drugs by changing liver enzyme activity. In a study in healthy people, itraconazole increased blood levels of another drug by 29.5% to 58% and lengthened how long that drug stayed in the body [5]. This kind of interaction can happen in dogs too.
Tell your veterinarian about everything your dog takes, including:
- Other antifungals
- Antibiotics
- Stomach acid reducers
- Steroids
- Seizure medications
- Pain medications
- Supplements and herbal products
Do not start or stop any other medication without asking your veterinarian first. Even over-the-counter products can interact.
Overdose and When to Call a Veterinarian or Poison Control
If your dog eats more itraconazole than prescribed, act right away. Signs of overdose can include severe vomiting, drooling, wobbliness, and lethargy. Do not wait for symptoms to appear.
Call your veterinarian or an emergency veterinary clinic immediately. You can also contact the ASPCA Animal Poison Control Center at (888) 426-4435 or the Pet Poison Helpline at (855) 764-7661. Both may charge a consultation fee.
Have this information ready:
- Your dog's weight
- The strength of the tablets or capsules
- How many were possibly eaten
- When it happened
- Any symptoms you have seen
Do not try to make your dog vomit unless a veterinarian tells you to. Some dogs should not be made to vomit, and the wrong method can cause harm.
Limitations and When to Contact a Veterinarian
This article covers general patterns. Your dog's case is specific, and only your veterinarian can judge what a symptom means for your dog.
Call your veterinarian the same day if your dog:
- Vomits more than once or cannot keep water down
- Refuses food for more than 24 hours
- Has diarrhea that lasts more than a day or contains blood
- Seems unusually tired, weak, or unsteady
- Develops yellow gums, eyes, or skin
Go to an emergency clinic now if your dog:
- Has trouble breathing or swelling of the face
- Collapses or cannot stand
- Has a seizure
- Shows severe weakness or unresponsiveness
- Has signs of bleeding that will not stop
Keep routine recheck visits even if your dog seems fine. Dose adjustments are common during treatment, and some problems only show up on blood work [1]. If your dog takes other medications for behavior or anxiety, our article on dog anxiety medication side effects can help you tell apart what is caused by which drug.
Frequently Asked Questions
Should I stop itraconazole if my dog vomits once?
A single mild vomit after a dose is not always a reason to stop. Give the next dose with a full meal and watch closely. If vomiting repeats, if your dog cannot keep water down, or if your dog seems dull or weak, stop the drug and call your veterinarian the same day.
Can itraconazole cause liver damage in dogs?
Liver enzyme changes are a known concern, and that is why veterinarians check blood work before and during treatment. Many changes are mild and picked up only on testing. Yellow gums, eyes, or skin are serious signs and need immediate veterinary care.
How long does it take for side effects to show up?
Stomach upset often appears within the first days to weeks of treatment. Liver changes can develop later and may not cause visible signs at all. This is one reason recheck blood work matters throughout treatment, not just at the start.
Is it safe to give itraconazole with other medications?
Not always. Itraconazole can raise or lower blood levels of other drugs, and a study in people showed it increased exposure to a companion drug by up to 58% [5]. Tell your veterinarian about every medication and supplement your dog takes before you start treatment.
What if I miss a dose?
Give the missed dose when you remember unless the next dose is almost due. If it is close, skip the missed dose and continue on schedule. Never give two doses at once to catch up, and tell your veterinarian if you are missing doses often.
Related Articles
- What Are the Side Effects of Antibiotics in Dogs?
- What Are the Side Effects of Trazodone for Dogs?
- Dog Anxiety Medication Side Effects: What to Watch For
- What Are the Side Effects of Bravecto for Dogs? What to Watch For
- What Are the Side Effects of Thyroid Medication for Dogs?
- What Are the Side Effects of Gabapentin for Dogs?
- Terbinafine for Dogs: Side Effects, Dosage, and Safety
- Miconazole for Dogs: Yeast, Paws, and Side Effects
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References
- Therapeutic drug monitoring of itraconazole in treatment of blastomycosis in dogs. Journal of veterinary internal medicine, 2026.
- Prolonged survival of 3 dogs with Prototheca bovis infection treated with posaconazole. Journal of veterinary internal medicine, 2026.
- Canine Protothecosis; Ocular Findings, Diagnosis, Treatment and Outcome in 8 Dogs. Veterinary ophthalmology, 2026.
- Bioassay and liquid chromatography-mass spectrometry are not equivalent in itraconazole therapeutic drug monitoring in dogs. American journal of veterinary research, 2026.
- Effect of itraconazole on pharmacokinetics of ZX-7101A tablets in healthy Chinese subjects. Frontiers in pharmacology, 2025.