Ketoconazole
Ketoconazolum
Also known as: Nizoral Β· Fungiconazole Β· ketoconazolum Β· R-41400
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
π NA β North Americaπ EU β Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Coccidioidomycosis (systemic form) | 5-10 mg/kg PO twice daily | PO | q12h | Minimum of 3-6 months | π NA |
| Coccidioidomycosis (CNS form) | 15-20 mg/kg PO twice daily | PO | q12h | Minimum of 3-6 months | π NA |
| Coccidioidomycosis (bony lesions or relapses) | 5 mg/kg PO every other day | PO | q48h | Lifelong | π NA |
| Coccidioidomycosis | 10-30 mg/kg PO divided twice a day | PO | q12h | 6-12 months | π NA |
| Blastomycosis | 10 mg/kg PO twice daily (15-20 mg/kg PO twice daily if CNS involvement) | PO | q12h | At least 3 months | π NA |
| Blastomycosis | 20 mg/kg/day PO once daily or divided twice daily; 40 mg/kg divided twice daily for ocular or CNS involvement | PO | q24h or q12h | At least 2-3 months or until remission | π NA |
| Histoplasmosis | 10 mg/kg PO once a day or twice a day | PO | q24h or q12h | At least 3 months | π NA |
| Histoplasmosis | 10-20 mg/day PO once daily or divided twice daily | PO | q24h or q12h | At least 2-3 months or until remission | π NA |
| Aspergillosis | 20 mg/kg PO | PO | Not specified | At least 6 weeks | π NA |
| Nasal aspergillosis | 10 mg/kg PO once daily (q24h) or 5 mg/kg PO q12h | PO | q24h or q12h | Many weeks; continue 1 month beyond last detection | π NA |
| Cryptococcosis | 10 mg/kg PO once daily or divided twice daily | PO | q24h or q12h | Maintenance | π NA |
| Fungal myocarditis | 10 mg/kg PO three times daily | PO | q8h | β | π NA |
| Candidiasis | 10 mg/kg PO once daily (q24h) or 5 mg/kg PO q12h | PO | q24h or q12h | Many weeks; continue 1 month beyond last detection | π NA |
| Sporotrichosis | 15 mg/kg PO q12h | PO | q12h | Many weeks; continue 1 month beyond last detection | π NA |
| Malassezia dermatitis (severe) | 5 mg/kg PO once daily to 10 mg/kg twice daily | PO | q24h to q12h | Until clinical signs abate and no organisms seen | π NA |
| Malassezia dermatitis | 5-10 mg/kg PO twice a day | PO | q12h | 30 days | π NA |
| Malassezia dermatitis | 5-10 mg/kg PO daily for 10 days, then every other day for an additional 10 days | PO | q24h then q48h | 20 days | π NA |
| Malassezia dermatitis | 5 mg/kg twice daily for 21-30 days, may increase to 10 mg/kg PO twice daily if poor response | PO | q12h | 21-30 days | π NA |
| Malassezia dermatitis | 2.5-10 mg/kg PO once daily (q24h) for 7-14 days; once a good response is seen taper to every other day (q48h) | PO | q24h then q48h | Until complete remission | π NA |
| Hyperadrenocorticism | 5-10 mg/kg PO twice daily initially; may increase to 15 mg/kg PO twice daily | PO | q12h | Long-term | π NA |
| Hyperadrenocorticism | 5 mg/kg q12h for 5-7 days, increase to 10 mg/kg q12h for 10-14 days; many require 15-20 mg/kg q12h | PO | q12h | Long-term | π NA |
| Hyperadrenocorticism (palliative) | 15 mg/kg PO q12h | PO | q12h | Long-term | π NA |
| Reduce cyclosporine dosage | 5-10 mg/kg PO per day | PO | q24h | Concurrent with cyclosporine | π NA |
| Perianal fistula (with cyclosporine) | 7.5 mg/kg PO twice daily | PO | q12h | β | π NA |
| Atopic dermatitis (with cyclosporine) | 5 mg/kg/day | PO | q24h | β | π NA |
| IMHA (with cyclosporine) | 10 mg/kg/day | PO | q24h | β | π NA |
- Blastomycosis: Used with amphotericin B
- Blastomycosis: Used with amphotericin B
- Histoplasmosis: Treat at least 30 days after complete resolution. Maintenance 5 mg/kg PO every other day indefinitely if relapse.
- Histoplasmosis: Used with amphotericin B
- Aspergillosis: May require long-term/maintenance therapy
- Nasal aspergillosis: Itraconazole somewhat more effective
- Cryptococcosis: Used with amphotericin B
- Malassezia dermatitis: Often used with therapeutic shampoos
- Hyperadrenocorticism: Monitor with ACTH stimulation test
- Perianal fistula (with cyclosporine): Given with cyclosporine 0.5-0.75 mg PO twice daily
- Atopic dermatitis (with cyclosporine): Given with cyclosporine 2.5 mg/kg/day
- IMHA (with cyclosporine): Allows reduction of cyclosporine dose
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Coccidioidomycosis | 10-30 mg/kg PO divided twice a day | PO | q12h | 6-12 months | π NA |
| Coccidioidomycosis | 50 mg per cat PO once daily; or 25-75 mg per cat q12-48h | PO | q24h or q12-48h | 9-12 months on average | π NA |
| Blastomycosis | 10 mg/kg q12h PO | PO | q12h | At least 60 days | π NA |
| Cryptococcosis | 10 mg/kg twice daily | PO | q12h | β | π NA |
| Aspergillosis | 10 mg/kg PO q12h | PO | q12h | β | π NA |
| Dermatophytosis | 10 mg/kg PO once daily with an acidic meal | PO | q24h | Prolonged; 2 weeks beyond clinical cure and negative cultures | π NA |
| Sporotrichosis | 5-10 mg/kg PO q12-24h | PO | q12-24h | 2-4 months on average | π NA |
- Coccidioidomycosis: Use in cats is controversial
- Blastomycosis: Used with amphotericin B
- Cryptococcosis: Can produce anorexia and debility at this dosage
- Dermatophytosis: Reserved for when griseofulvin ineffective or not tolerated
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections (Rabbits) | 10-40 mg/kg per day PO | PO | q24h | 14 days | π NA |
| Systemic mycoses/candidiasis (Hamsters, Gerbils, Mice, Rats, Guinea pigs, Chinchillas) | 10-40 mg/kg per day PO | PO | q24h | 14 days | π NA |
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Severe refractory candidiasis in Psittacines | 5-10 mg/kg as a gavage twice daily | PO (gavage) | q12h | 14 days | π NA |
| Susceptible fungal infections (most species) | 200 mg/L | PO (water) | Continuous | 7-14 days | π NA |
| Susceptible fungal infections (most species) | 10-20 mg/kg | PO (feed) | Daily | 7-14 days | π NA |
| Susceptible fungal infections (Moluccan Cockatoos) | 20-30 mg/kg PO twice daily | PO | q12h | β | π NA |
| Susceptible fungal infections (Ratites) | 5-10 mg/kg PO once daily | PO | q24h | β | π NA |
- Severe refractory candidiasis in Psittacines: Dissolve in 0.2 mL 1 N HCl and add 0.8 mL water
- Susceptible fungal infections (most species): Dissolve in acid prior to adding to water
- Susceptible fungal infections (most species): Add to favorite food or mash
Reptiles
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible infections (most species) | 15-30 mg/kg PO once daily | PO | q24h | 2-4 weeks | π NA |
| Fungal shell diseases in turtles/tortoises | 25 mg/kg PO once a day | PO | q24h | 2-4 weeks | π NA |
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Susceptible yeasts and Aspergillus spp | 5 mg/kg PO once daily | PO | q24h | β | π NA |
| Scopulariopsis pneumonia | 30 mg/kg q12h | NG tube | q12h | β | π NA |
- Susceptible yeasts and Aspergillus spp: Using commercial oral solution
- Scopulariopsis pneumonia: Administered via NG tube mixed with 0.2 Normal hydrochloric acid
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Ketoconazole is a first-generation imidazole antifungal agent. While it has been largely superseded by newer triazoles (like itraconazole and fluconazole) due to their better safety profiles and enhanced efficacy, ketoconazole remains a cost-effective option for treating certain systemic mycoses (e.g., Blastomyces, Histoplasma, Coccidioides, and Malassezia dermatitis).
βClinical Pearl:β Beyond its antifungal properties, ketoconazole is a potent inhibitor of mammalian cytochrome P450 enzymes. This unique characteristic is frequently leveraged off-label in veterinary medicine for two main purposes:
- βDrug Sparing:β To reduce the required dose (and cost) of expensive drugs like cyclosporine by inhibiting its hepatic metabolism.
- βEndocrine Therapy:β As a medical management option for βcanine hyperadrenocorticism (Cushing's disease)β by reversibly inhibiting adrenal steroidogenesis.
βNote:β The use of ketoconazole in cats is highly controversial due to a higher prevalence of gastrointestinal and hepatic toxicity; many clinicians prefer itraconazole for feline patients.
Mechanism of action
βAntifungal Action:β Ketoconazole inhibits lanosterol 14Ξ±-demethylase, a fungal cytochrome P450 enzyme β blocks the conversion of lanosterol to ergosterol β depletion of ergosterol in the fungal cell membrane β accumulation of toxic intermediate sterols β increased cellular membrane permeability and cell death. It is primarily fungistatic but can be fungicidal at high concentrations or prolonged exposures.
βEndocrine/Metabolic Action:β It reversibly inhibits mammalian cytochrome P450 enzymes (specifically CYP11A1 and CYP17) β blocks the synthesis of adrenal and gonadal steroids β decreases cortisol and testosterone production.
βImmunomodulatory Action:β Inhibits 5-lipooxygenase, providing mild anti-inflammatory effects, and suppresses T-lymphocyte proliferation.
Safety & warnings
Contraindications
- Known hypersensitivity to ketoconazole
- Controversial/Contraindicated in cats (due to toxicity risks)
- Concurrent use with cisapride or ivermectin (in dogs)
- Hepatic insufficiency
- Pregnancy (due to possible teratogenic effects)
Adverse effects
- Anorexia (most common, especially in cats)
- Vomiting
- Diarrhea
- Hepatic toxicity (cholangiohepatitis, increased liver enzymes)
- Thrombocytopenia (rare)
- Reversible lightening of haircoat
- Transient suppression of gonadal and adrenal steroid synthesis
- Infertility in male dogs (reversible)
- Hepatotoxicity
- Alterations in hair-coat colour
- Thrombocytopenia (at high doses)
- Adrenal insufficiency (at high doses)
- Cataract development (in dogs)
- Teratogenic effects
Precautions
Use with caution in patients with hepatic disease or thrombocytopenia. Ketoconazole is a known teratogen and embryotoxin; weigh risks vs. benefits in pregnant animals. It may cause reversible infertility in male dogs by decreasing testosterone synthesis. Dogs undergoing high-dose antifungal therapy may need additional glucocorticoid support during periods of acute stress due to adrenal suppression.
Drug interactions
May produce a disulfiram-like reaction (vomiting)
May reduce oral absorption of ketoconazole; administer at least 1 hour before or 2 hours after
Ketoconazole may reduce metabolism and increase adverse effects
Ketoconazole may increase levels
Plasma concentrations may be elevated
Ketoconazole may increase levels
Ketoconazole may increase levels
Ketoconazole may increase cisapride levels and possibility for toxicity; use together contraindicated
Ketoconazole may inhibit metabolism; potential for increased adverse effects
Ketoconazole may inhibit metabolism; potential for increased toxicity
Increased cyclosporine levels (often used therapeutically to reduce cyclosporine dose)
Ketoconazole may increase digoxin levels
Ketoconazole may increase fentanyl or alfentanil levels
Increased gastric pH may reduce ketoconazole absorption
Should be used cautiously together due to additive hepatotoxicity risk
May affect ketoconazole levels; concomitant use not recommended
Ketoconazole may increase risk for neurotoxicity; should never be used together in dogs
May increase ketoconazole concentrations
Not recommended together; adrenolytic effects of mitotane may be inhibited by ketoconazole
May decrease ketoconazole levels
Increased gastric pH may reduce ketoconazole absorption
Ketoconazole may increase quinidine levels
May decrease ketoconazole levels; ketoconazole may increase rifampin levels
May reduce absorption of ketoconazole
Ketoconazole may increase levels; hypoglycemia possible
Ketoconazole may decrease serum theophylline concentrations; monitor levels
Ketoconazole may inhibit vinca alkaloid metabolism and increase levels
Ketoconazole may cause increased prothrombin times
Ketoconazole increases blood levels of ciclosporin (used therapeutically to reduce ciclosporin dose requirements)
Used synergistically in systemic fungal disease, allowing for a reduced dose of amphotericin B
Increases gastric pH, which impairs the absorption of ketoconazole; stagger dosing
Increases gastric pH, which impairs the absorption of ketoconazole; stagger dosing
Increases gastric pH, which impairs the absorption of ketoconazole; stagger dosing
Ketoconazole extends the activity of methylprednisolone
Inhibits the metabolism of antihistamines (extrapolated from human data)
Inhibits the metabolism of oral hypoglycaemics (extrapolated from human data)
Inhibits the metabolism of antiepileptics (extrapolated from human data)
Monitoring
- Liver enzymes with chronic therapy (at least every 1-2 months)
- CBC with platelets
- Clinical efficacy
- Adverse effects (GI signs, jaundice)
- Liver function tests (routine monitoring recommended)
- Platelet count (if high doses are used)
- Adrenal function/clinical signs of hypoadrenocorticism
Pharmacokinetics
Half-life
Absorption
Highly variable oral bioavailability in dogs (4-89%). Absorption is enhanced in an acidic environment and may be increased with food. Poor oral absorption of tablets in horses, but increases to 23% if given with hydrochloric acid, and 60% with oral solution.
Distribution
Distributed into bile, cerumen, saliva, urine, synovial fluid, and CSF (CSF levels <10% of serum). High levels in liver, adrenals, and pituitary gland. 84-99% bound to plasma proteins. Crosses the placenta and is found in milk.
Metabolism
Extensively metabolized by the liver into several inactive metabolites.
Elimination
Metabolites are excreted primarily into the feces via the bile. About 13% is excreted into the urine (only 2-4% unchanged).
Overdose
No reports of acute toxicity associated with overdosage were located. The oral LD50 in dogs is >500 mg/kg. In the event of an acute overdose, employ supportive measures, including gastric lavage with sodium bicarbonate.
Available products
Formulations
- Oral tablets
- Oral suspension (compounded)
- Topical preparations
- 200 mg oral tablet
Veterinary
- None for systemic use
- Fungiconazole 200 mg tablet
Human-labeled
- Ketoconazole Tablets: 200 mg (scored)
Regulatory status
POM-V classification
POM-V (Prescription Only Medicine - Veterinarian)
No regulatory data for: πΊπΈ US Β· ππ° HK Β· πΉπΌ TW Β· π―π΅ JP Β· π°π· KR Β· π¦πΊ AU
Storage & stability
Store tablets at room temperature in well-closed containers. Compounded oral suspensions (20 mg/mL) retain >95% potency for 60 days when stored at 5Β°C or 25Β°C and protected from light.
Client information
- βAdministration:β Give this medication with food to increase absorption and reduce stomach upset. If your pet develops vomiting or loss of appetite, dividing the daily dose may help.
- βSide Effects:β Watch for loss of appetite, vomiting, or diarrhea. If these occur, contact your veterinarian. In cats, these side effects are more common.
- βCoat Changes:β You might notice a reversible lightening of your pet's haircoat during treatment.
- βCommitment:β Fungal infections often require months of continuous treatment. Do not stop the medication early even if your pet looks better, as the infection can easily return.
- βWarning:β Inform your vet of all other medications your pet is taking, as ketoconazole interacts with many drugs.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerβs current label.