Voriconazole: veterinary dose and monograph

At a glance

Drug class

Antifungal

Also known as

Vfend, Voritek, Vorizol

Species with doses

Dogs, Cats, Horses and Birds

General dose range

4–5 mg/kg PO q12h — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Invasive / sino-nasal / disseminated aspergillosis (dogs)
• CNS or ocular fungal infection (good penetration)
• Fungal keratitis (topical 1 % solution)
• Aspergillosis and other mycoses in birds/raptors

Voriconazole dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Aspergillosis / systemic mycosis: Papich 5e: 5–6 mg/kg q12h PO (research dogs), but 2.5–3.3 mg/kg q12h produced adequate levels in a clinical report — safety of repeated dosing not confirmed. Plumb’s p.1172: coccidioidomycosis 4 mg/kg PO q12h. Therapeutic drug monitoring ideal; monitor liver enzymes.

Cats

• Systemic mycosis (use with great caution): Papich 5e: loading 25 mg per cat (4.2–4.6 mg/kg), then 12.5 mg (2–2.3 mg/kg) every other day — accumulation occurs. Plumb’s p.1172: cats given 10 mg/kg once daily had significant systemic (neurological) reactions (Smith & Hoffman 2010).

Horses

• Systemic mycosis: Papich 5e: 2–4 mg/kg q24h or 3 mg/kg q12h PO; 1.5 mg/kg q24h IV. Plumb’s p.1172 (Davis 2008): 3 mg/kg PO q24h for aspergillosis; 4–5 mg/kg probably needed for Fusarium. Topical 1% solution is used for fungal keratitis.

Birds

• Aspergillosis (raptors/psittacines): Papich 5e: 10 mg/kg q12h PO as a 0.5 mg/mL suspension. Plumb’s p.1172: aspergillosis 12.5 mg/kg PO twice daily for 60–90 days, or nebulised 1 mg/mL for 60 min daily (Black 2008); Amazon parrots 18 mg/kg PO q8h for 11 days was safe (Guzman 2010). Species differences in kinetics.

Contraindications

Cats — avoid (severe neurotoxicity, ataxia, and toxicity at standard doses). Significant hepatic impairment. Concurrent drugs with dangerous CYP interactions (potent CYP inhibitor/substrate). Pregnancy (teratogenic). Known azole hypersensitivity.

Species-specific warnings

Cats: AVOID — cats develop severe neurotoxicity (ataxia, paraparesis), hepatotoxicity and other toxicity at standard doses; use safer azoles (itraconazole/fluconazole) in cats.

Adverse effects

• Hepatotoxicity (raised liver enzymes)
• Neurotoxicity — ataxia, visual disturbance, hallucination-type signs (severe/common in CATS)
• GI upset, anorexia
• Photosensitivity / skin reactions
• Visual disturbances (transient)

Drug interactions

• Potent CYP inhibitor: raises levels of cyclosporine, tacrolimus, benzodiazepines, vincristine, opioids, etc.
• CYP inducers (phenobarbital, rifampin): markedly lower voriconazole levels
• QT-prolonging drugs: additive arrhythmia risk
• Many contraindicated combinations (as in human labelling) — review co-medications carefully

Pregnancy and lactation

Contraindicated/avoid in pregnancy — azole teratogenicity.

Monitoring

• Liver enzymes (baseline and during therapy)
• Neurologic/visual status (especially early; mandatory caution in cats)
• Therapeutic drug monitoring (trough levels) where available — variable kinetics
• Review co-medications for CYP/QT interactions

Toxicity and overdose

Hepatotoxicity and dose-related NEUROTOXICITY (visual changes, ataxia, encephalopathy) are key; kinetics are non-linear and variable, so toxicity can develop unpredictably (therapeutic drug monitoring helps). CATS are especially sensitive — neurotoxicity and toxicity occur at otherwise standard doses, so it is generally avoided in cats.

Management: No specific antidote. Discontinue; supportive care and hepatoprotection (SAMe/silybin) for hepatotoxicity; manage neurologic signs supportively. Decontaminate large recent ingestions. Effects resolve slowly given variable kinetics; consider drug-level testing.

Clinical pearls

• The azole of choice for invasive ASPERGILLOSIS and CNS/ocular fungal infection — more potent against moulds with better penetration than itraconazole/fluconazole
• AVOID in cats — they are exquisitely sensitive to voriconazole neurotoxicity at standard doses
• Variable, non-linear kinetics make therapeutic drug monitoring valuable; watch the liver
• A heavyweight CYP interactor — meticulously review all co-medications before starting
• Birds need much higher mg/kg than mammals (species kinetic differences)

Mechanism of action

Like other azoles it inhibits fungal cytochrome-P450 14-α-demethylase (CYP51), blocking ergosterol synthesis and damaging the fungal cell membrane (fungistatic, fungicidal against some moulds). Its structure gives enhanced potency against Aspergillus and other moulds and superior CNS/ocular penetration. It is both a substrate and a potent inhibitor of mammalian CYP enzymes, underlying its extensive drug interactions and variable kinetics.

Formulations and products

• 50 mg tablet
• 200 mg tablet
• Injection 200 mg vial (reconstitute)
• Ophthalmic solution 1 % (compounded)
• Vfend — 50 / 200 mg tablet; 200 mg vial, Tablet / injection (human-label)
• Voritek / Vorizol — 50 / 200 mg tablet, Tablet (human-label)

Storage

Tablets: 15–30 °C, dry. Reconstituted IV/ophthalmic per label (refrigerate, limited shelf-life). Protect from light.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other antifungals

• Miconazole
• Nystatin
• Posaconazole
• Terbinafine

Frequently asked questions