# Voriconazole: veterinary dose and monograph

> Voriconazole is a veterinary antifungal. A second-generation triazole antifungal with a BROAD spectrum and excellent tissue, CNS and ocular penetration — used for invasive ASPERGILLOSIS (including sino-nasal and disseminated), resistant/CNS fungal infections, and fungal… Indications include invasive / sino-nasal / disseminated aspergillosis (dogs); CNS or ocular fungal infection (good penetration); fungal keratitis (topical 1 % solution). This monograph lists 4 reference doses for dogs, cats, horses and birds, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/voriconazole · Last reviewed: 2026-10-01

## 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

*Voriconazole doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Aspergillosis / systemic mycosis | 2.5–6 mg/kg | PO | q12h | — |

- 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

*Voriconazole doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Systemic mycosis (use with great caution) | 12.5–25 mg/cat | PO | 25 mg once, then 12.5 mg every other day | — |

- 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

*Voriconazole doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Systemic mycosis | 2–5 mg/kg | PO | q12–24h | — |

- 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

*Voriconazole doses for birds*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Aspergillosis (raptors/psittacines) | 10–18 mg/kg | PO | q8–12h | — |

- 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

> **Caution:** 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

> **Caution:** 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](https://vetmasterji.com/drugs/miconazole)
- [Nystatin](https://vetmasterji.com/drugs/nystatin)
- [Posaconazole](https://vetmasterji.com/drugs/posaconazole)
- [Terbinafine](https://vetmasterji.com/drugs/terbinafine)

## Frequently asked questions

### What is the dose of Voriconazole for dogs?

Reference doses for Voriconazole in dogs: 2.5–6 mg/kg PO q12h (Aspergillosis / systemic mycosis). Confirm against the label and the patient before use.

### What is the dose of Voriconazole for cats?

Reference doses for Voriconazole in cats: 12.5–25 mg/cat PO 25 mg once, then 12.5 mg every other day (Systemic mycosis (use with great caution)). Confirm against the label and the patient before use.

### What is the dose of Voriconazole for horses?

Reference doses for Voriconazole in horses: 2–5 mg/kg PO q12–24h (Systemic mycosis). Confirm against the label and the patient before use.

### When should Voriconazole not be used?

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.

### What are the side effects of Voriconazole in animals?

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

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.