What Is Ketoconazole and What Does It Treat?
Ketoconazole is a broad-spectrum azole antifungal medication used in dogs to treat infections caused by yeasts and fungi. It belongs to the same family as itraconazole and fluconazole, and is known by the human brand name Nizoral. In dogs it is used off-label but is a long-established veterinary antifungal.
Ketoconazole works by interfering with ergosterol, a vital building block of the fungal cell membrane. Without intact ergosterol the fungal cell membrane becomes leaky and the organism cannot survive or multiply. The most common reasons a veterinarian prescribes oral ketoconazole for a dog include:
- _Malassezia_ dermatitis — overgrowth of yeast on the skin and in the ears, causing itching, odour, greasy skin and recurrent ear infections.
- Ringworm (dermatophytosis) — a fungal infection of the skin, hair and nails.
- Systemic fungal infections — serious deep infections such as blastomycosis, histoplasmosis and coccidioidomycosis.
Ketoconazole has a second, separate use that is worth understanding: because it suppresses the production of steroid hormones, including cortisol, it is sometimes used as part of the management of Cushing’s disease (hyperadrenocorticism), and it can deliberately be combined with cyclosporine to reduce the dose of that expensive drug. For more background on this drug, see PuppaDogs’ guide to ketoconazole for dogs, and the overview of Cushing’s supplements for dogs.
Ketoconazole is a prescription medicine with real potential for liver side effects. Use the calculator above to understand the typical dose range, but the actual prescription must come from your veterinarian.
How the Ketoconazole Dosage Calculator Works
The calculator converts your dog’s weight into an estimated dose using standard milligram-per-kilogram ranges, adjusted for what is being treated. It then:
- Shows the daily dose and per-dose amount for once- or twice-daily dosing.
- Converts the dose into 200 mg tablets, or flags when the dose is too small for a tablet and needs a compounded liquid.
- Applies caution and contraindication flags for liver disease, pregnancy and concurrent medications.
Enter your dog’s weight, choose the indication, select the dosing frequency and the form you have, tick any health considerations, then press Calculate Dose.
How Ketoconazole Doses Are Calculated for Dogs
Standard Dose Range
Published veterinary dosing for oral ketoconazole in dogs is approximately:
- Skin and ear yeast (_Malassezia_): around 5 mg/kg once daily
- Ringworm and systemic fungal infections: around 10 mg/kg per day, given once daily or split into two doses
The total daily dose generally falls in the 5–10 mg/kg range, with deep or stubborn infections managed at the higher end under veterinary direction. The calculator uses these rates and lets you choose once- or twice-daily dosing.
Factors That Affect the Dose
- Type and depth of infection — surface yeast needs less than a deep systemic mycosis.
- Liver function — ketoconazole is metabolised by the liver and can be hepatotoxic; liver disease is a strong reason to avoid it.
- Stomach acidity — ketoconazole needs an acidic stomach to dissolve and absorb, so it must be given with food and kept away from antacids.
- Other medications — ketoconazole is a powerful inhibitor of drug-metabolising enzymes and can dangerously raise the levels of many other drugs.
Ketoconazole Dosage Chart for Dogs
This chart shows the typical daily dose. It is a reference only — your veterinarian’s prescription takes priority.
| Dog weight | Skin yeast (~5 mg/kg/day) | Ringworm / systemic (~10 mg/kg/day) |
|---|---|---|
| 10 lb (4.5 kg) | ~23 mg | ~45 mg |
| 20 lb (9 kg) | ~45 mg | ~91 mg |
| 40 lb (18 kg) | ~91 mg | ~181 mg |
| 60 lb (27 kg) | ~136 mg | ~272 mg |
| 80 lb (36 kg) | ~181 mg | ~363 mg |
Ketoconazole Forms and Strengths
- Oral tablets: 200 mg (scored). Human-labelled tablets are used off-label in dogs.
- Compounded liquids or capsules: prepared by a compounding pharmacy for small dogs or dogs that need a non-standard dose.
- Topical products: ketoconazole shampoos, wipes and creams are widely used for skin and ear yeast and may be combined with, or used instead of, oral treatment.
How to Give Ketoconazole to Your Dog
- Always give with food. Food and normal stomach acid greatly improve absorption.
- Avoid antacids and acid reducers around dosing time — drugs such as famotidine, omeprazole or antacid gels reduce ketoconazole absorption. If your dog needs those, tell your vet.
- Be consistent with timing each day.
- Hide the tablet in a pill pocket or small piece of food.
- Finish the full course. Fungal infections are slow to clear, and stopping early invites relapse.
- Missed dose: give it when you remember unless the next dose is close, then skip it — never double up.
Side Effects and Safety Warnings
The most common side effects are gastrointestinal: reduced appetite, nausea and vomiting. Giving the medication with food helps. Other possible effects include lightening of the hair coat and, with long-term use, a link to cataracts.
The most important risk is liver toxicity (hepatotoxicity). Contact your veterinarian promptly if your dog shows yellowing of the gums or eyes (jaundice), dark urine, marked loss of appetite, persistent vomiting or unusual lethargy. For courses lasting more than a couple of weeks, your vet will usually monitor liver enzyme bloodwork.
When Ketoconazole Should Be Avoided or Used With Caution
- Liver disease — generally avoided; a different antifungal is safer.
- Pregnant, nursing or breeding dogs — ketoconazole can cause birth defects and disrupts reproductive hormones; it should not be used.
- Dogs on interacting medications — see below.
Drug Interactions
Ketoconazole strongly inhibits the CYP3A enzyme system and P-glycoprotein, which means it slows the body’s clearance of many other drugs and can raise their blood levels to toxic ranges. Notable interactions include cyclosporine, certain sedatives and tranquilizers, some heart and blood-pressure medications, and other drugs. This effect is sometimes used deliberately and carefully by vets, but it also means you must give your veterinarian a complete list of everything your dog takes. Where a safer option is appropriate, your vet may choose a newer antifungal such as fluconazole.
Overdose — Signs and What to Do
A single mild overdose often causes only stomach upset, but large or repeated overdoses raise the risk of liver injury and, potentially, neurological signs. If you suspect an overdose or accidental ingestion, contact your veterinarian or an animal poison control service immediately and bring the packaging.
Treatment Duration and Monitoring
Ketoconazole is rarely a short course. Skin and ear yeast infections typically need 2–4 weeks; ringworm and deep systemic mycoses often need several months, continued well past the point where the dog looks better. Expect your vet to schedule recheck examinations and liver bloodwork, and possibly repeat skin or fungal testing, to confirm the infection has truly cleared before stopping.
Conclusion
Ketoconazole is an effective, well-established antifungal for canine yeast, ringworm and systemic fungal infections, dosed at roughly 5–10 mg/kg per day depending on the infection. The calculator above gives you an evidence-based estimate and converts it into tablets, while flagging the situations — liver disease, pregnancy, interacting drugs — that make it unsafe. Because ketoconazole carries a genuine risk of liver toxicity and has been overtaken by gentler antifungals for many infections, it should always be prescribed, dosed and monitored by your veterinarian.
Frequently Asked Questions
How much ketoconazole can I give my dog?
Oral ketoconazole for dogs is usually dosed at about 5 mg/kg per day for skin and ear yeast (Malassezia) infections, and around 10 mg/kg per day for ringworm and systemic fungal infections, given once daily or split into two doses. The exact dose and course length must be set by your veterinarian. Use the calculator above for an estimate only.
What is ketoconazole used for in dogs?
Ketoconazole is an antifungal used in dogs to treat yeast (Malassezia) skin and ear infections, ringworm, and serious systemic fungal infections such as blastomycosis. Because it also lowers steroid hormone production, it is sometimes used as part of managing Cushing’s disease and to reduce the required dose of cyclosporine.
Does ketoconazole need to be given with food?
Yes. Ketoconazole should be given with food, because a meal and a normal-acid stomach significantly improve its absorption. Antacids and acid-reducing medications lower absorption, so if your dog takes those, tell your veterinarian so dosing can be separated or an alternative chosen.
What are the side effects of ketoconazole in dogs?
The most common side effects are loss of appetite, nausea and vomiting, which are eased by giving the drug with food. Lightening of the coat can occur, and long-term use has been linked to cataracts. The most serious risk is liver toxicity – contact your vet immediately for jaundice, dark urine, persistent vomiting or marked lethargy.
How long does a dog need to take ketoconazole?
It depends on the infection. Skin and ear yeast infections usually need 2-4 weeks of treatment, while ringworm and deep systemic fungal infections often require several months and should be continued past the point where the dog appears better. Your veterinarian decides the course length, usually with rechecks and liver bloodwork.
Is ketoconazole or fluconazole better for dogs?
Both are azole antifungals, but for many infections newer drugs such as fluconazole and itraconazole have largely replaced ketoconazole because they tend to be gentler on the liver and have more predictable absorption. Ketoconazole is still useful and less expensive in some cases. Your veterinarian will choose based on the type of infection, your dog’s liver health and cost.
References & Further Reading
The dosing ranges and safety information on this page are drawn from the following veterinary references. Always defer to your own veterinarian and the manufacturer’s label for your specific product.
- Plumb DC. Plumb’s Veterinary Drug Handbook. 10th ed. Hoboken, NJ: Wiley-Blackwell, 2023 – ketoconazole monograph.
- Merck Veterinary Manual. Antifungal drugs – azoles; antifungals for integumentary disease in animals. merckvetmanual.com.
- American Animal Hospital Association (AAHA). 2023 Management of Allergic Skin Diseases in Dogs and Cats Guidelines – oral antifungal medication doses. aaha.org.
- Clinician’s Brief. Antifungal drugs to treat Malassezia pachydermatis in dogs and cats. cliniciansbrief.com.
- PuppaDogs. Ketoconazole for Dogs: Benefits, Dosage, Side Effects, and More. puppadogs.com.
