Fluconazole
Fluconazole (UK-49858)
Also known as: Diflucan Β· UK-49858 Β· Fluconazolum
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 |
|---|---|---|---|---|---|
| Cryptococcosis, candidiasis, systemic mycoses, nasal aspergillosis | 2.5-5 mg/kg PO or IV q12-24h | PO/IV | q12-24h | 56-84 days | π NA |
| Fungal meningitis | 5-8 mg/kg PO or IV q12h OR 8-12 mg/kg PO or IV once daily (q24h) | PO/IV | q12h or q24h | 56-84 days | π NA |
| Urinary candidiasis | 5-10 mg/kg PO q24h | PO | q24h | 21-42 days | π NA |
| Urinary Candida glabrata infection | 12 mg/kg PO once daily | PO | q24h | 21-42 days | π NA |
| Cryptococcosis | 5 mg/kg PO once or twice daily | PO | q12h or q24h | At least 2 months beyond resolution of clinical signs | π NA |
| Blastomycosis | 5 mg/kg PO q12h | PO | q12h | 60 days | π NA |
| Cryptococcosis | 5-15 mg/kg PO q12-24h | PO | q12-24h | 6-10 months | π NA |
| Treatment of Malassezia (may be safer than itraconazole or ketoconazole in dogs with hepatic disease) | 5 mg/kg PO once daily | PO | q24h | β | π NA |
| Systemic treatment of Malassezia dermatitis | 5 mg/kg PO once daily | PO | q24h | β | π NA |
| Recurrent Malassezia dermatitis | 5 mg/kg PO 3 times per week | PO | 3 times per week | β | π NA |
| Systemic treatment of Malassezia dermatitis | 2-5 mg/kg PO once daily (q24h) | PO | q24h | β | π NA |
| Nasal aspergillosis (alternative to itraconazole or terbinafine) | 2.5-5 mg/kg PO q12h | PO | q12h | 3-6 months | π NA |
- Cryptococcosis, candidiasis, systemic mycoses, nasal aspergillosis: Often treat neurologic ocular cryptococcosis for at least 12 weeks or 2 weeks after CSF exam shows resolution
- Nasal aspergillosis (alternative to itraconazole or terbinafine): Cure rates up to 60%
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Nasal or dermal cryptococcosis | 5-10 mg/kg PO q12-24h, or 10 mg/kg PO q24h | PO | q12-24h | β | π NA |
| CNS, intraocular, or multisystemic cryptococcosis | 50-100 mg/cat PO or IV q12h | PO/IV | q12h | β | π NA |
| CNS, intraocular or multisystemic mycoses | 50 mg/cat PO once daily (q24h) | PO | q24h | β | π NA |
| Cryptococcosis | 50 mg (total dose) PO twice daily | PO | q12h | 1 month beyond resolution of clinical signs | π NA |
| Cryptococcosis | 50 mg (total dose) PO twice daily | PO | q12h | At least 2 months beyond resolution of clinical signs | π NA |
- Nasal or dermal cryptococcosis: For most infections, 50 mg/cat PO once daily achieves adequate therapeutic levels
- CNS, intraocular, or multisystemic cryptococcosis: Often treat neurologic ocular cryptococcosis for at least 12 weeks or 2 weeks after CSF exam shows resolution
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| General (Rabbits) | 25-43 mg/kg slow IV q12h | IV | q12h | β | π NA |
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Candidiasis (cockatoos, parrots) | 20 mg/kg PO q24-48h or 10 mg/kg PO q24h | PO | q24-48h | β | π NA |
| Candidiasis (cockatiels) | 10 mg/kg fluconazole PO suspension and 100 mg/mL fluconazole treated drinking water | PO | β | β | π NA |
| Alternate treatment of aspergillosis | 5-10 mg/kg PO once daily | PO | q24h | up to 6 weeks | π NA |
- Candidiasis (cockatoos, parrots): Likely effective for C. albicans. C. galabrata and C. papasilosis may have higher MICs.
- Candidiasis (cockatiels): Maintained plasma levels above the MIC for most strains of Candida albicans
- Alternate treatment of aspergillosis: With or after amphotericin B
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| C. immitis infection or Candida bacteremia | Loading dose of 14 mg/kg followed by 5 mg/kg PO once daily | PO | q24h | β | π NA |
| Fungal keratitis | 1 mg/kg PO q24h | PO | q24h | β | π NA |
- Fungal keratitis: Anecdotal reports of successful treatment
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Fluconazole is a systemic triazole antifungal agent. Unlike older first-generation azoles (such as ketoconazole), it is highly hydrophilic, allowing for excellent penetration into the βcentral nervous system (CSF)β, eyes, and urinary tract.
βClinical Pearl:β Fluconazole does not require an acidic gastric environment for absorption, making its oral bioavailability highly reliable even in patients receiving antacid therapy. Furthermore, it has a significantly lower affinity for mammalian cytochrome P450 enzymes compared to ketoconazole, meaning it has minimal impact on mammalian steroid hormone synthesis and generally fewer side effects.
Mechanism of action
Fluconazole acts by inhibiting the fungal cytochrome P450-dependent enzyme lanosterol 14-Ξ±-demethylase.
Lanosterol β (blocked by fluconazole) β Ergosterol
This depletion of ergosterol disrupts the synthesis of the fungal cell membrane, increasing its permeability and causing leakage of essential cellular contents. It also impairs the uptake of purine and pyrimidine precursors. Fluconazole is primarily fungistatic.
Safety & warnings
Contraindications
- Hypersensitivity to fluconazole or other azole antifungals
- Budgerigars (reportedly toxic)
- Pregnant animals
- Lactating animals
Adverse effects
- Inappetence
- Vomiting
- Diarrhea
- Hepatotoxicity (rare)
- Headache (humans)
- Increased liver enzymes (humans)
- Exfoliative skin disorders (humans)
- Thrombocytopenia (humans)
- Nausea
- Diarrhoea
Precautions
Use with caution in patients with hepatic impairment. Because fluconazole is eliminated primarily by the kidneys, doses or dosing intervals may need to be adjusted in patients with renal impairment. Safety during pregnancy has not been established (FDA Category C); use with caution in nursing dams as it is excreted in milk. Reportedly toxic to budgerigars.
Drug interactions
May be antagonistic against Aspergillus or Candida; clinical importance unclear
Plasma concentrations of buspirone may be elevated
May increase cisapride levels and the possibility for toxicity
May inhibit the metabolism of corticosteroids; potential for increased adverse effects
May inhibit the metabolism of cyclophosphamide and its metabolites; potential for increased toxicity
Increases cyclosporine levels; dosage of cyclosporine may need to be decreased by 29%-51%
Increased fluconazole concentrations
May increase fentanyl levels
Increased midazolam levels and effects
May increase NSAID plasma levels; increased risk for adverse effects
Increased risk for cardiotoxicity
May decrease fluconazole efficacy; fluconazole may increase rifampin levels
Increased theophylline concentrations
May exacerbate the effects of tricyclic antidepressants (e.g., clomipramine, amitriptyline)
May increase levels of agents like glipizide or glyburide; hypoglycemia possible
May inhibit vinca alkaloid metabolism
May cause increased prothrombin times
Fluconazole inhibits cytochrome P450-dependent liver enzymes, which may increase plasma theophylline concentrations.
Co-administration has led to terfenadine toxicity in humans.
Fluconazole increases ciclosporin blood levels.
Monitoring
- Clinical efficacy
- Liver function tests (occasional, with long-term therapy)
- Liver enzyme panel (ALT, AST, ALP, Bilirubin) prior to and during prolonged therapy
- Renal function (BUN, Creatinine)
- Resolution of clinical signs of fungal infection
- Therapeutic drug monitoring for concurrent medications like ciclosporin or theophylline
Pharmacokinetics
Absorption
Rapidly and nearly completely absorbed (90%) after oral administration. Gastric pH or the presence of food do not appreciably alter oral bioavailability.
Distribution
Low protein binding and widely distributed throughout the body. Penetrates well into the CSF, eye, and peritoneal fluid.
Metabolism
Minimal hepatic metabolism compared to other azole antifungals.
Elimination
Eliminated primarily via the kidneys and achieves high concentrations in the urine.
Overdose
There is limited information on acute toxicity in domestic animals. In rodents, massive overdoses (1-2 g/kg) caused respiratory depression, salivation, lacrimation, urinary incontinence, and cyanosis, leading to death within several days.
βTreatment:β If a massive overdose occurs, consider gut emptying (emesis or gastric lavage) if recent, and provide supportive therapy as required. Fluconazole may be removed by hemodialysis or peritoneal dialysis.
Available products
Formulations
- Tablets
- Powder for oral suspension
- Injection
- 150 mg oral capsule
- 200 mg oral capsule
- 40 mg/ml oral suspension
- 2 mg/ml injectable solution
Human-labeled
- Fluconazole Oral Tablets: 50 mg, 100 mg, 150 mg, & 200 mg
- Fluconazole Powder for Oral Suspension: 10 mg/mL & 40 mg/mL (when reconstituted)
- Fluconazole Injection: 2 mg/mL in 100 mL or 200 mL bottles or Viaflex Plus
- Diflucan 50 mg, 150 mg, 200 mg capsules
- Diflucan 40 mg/ml oral suspension
- Diflucan 2 mg/ml injectable solution
Regulatory status
POM (Prescription Only Medicine)
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
Tablets should be stored at temperatures less than 30Β°C in tight containers. Injection should be stored at 5-30Β°C (5-25Β°C for Viaflex bags); avoid freezing. Do not add additives to the injection.
Client information
- βPatience is Key:β Fungal infections take a long time to clear. Treatment often lasts for several weeks to months. Do not stop the medication early even if your pet looks better, as the infection can relapse.
- βAdministration:β Fluconazole is very well absorbed whether given with food or on an empty stomach.
- βWatch for Side Effects:β While generally very safe, watch for loss of appetite, vomiting, or diarrhea. Contact your veterinarian if these occur.
- βCost:β Because treatment is prolonged, the cost can add up, though generic options have made it more affordable.
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.