Griseofulvin: veterinary dose and monograph

At a glance

Drug class

Antifungal

Also known as

Grisovin, Fulcin, Griseofulvin microsize/ultramicrosize

Species with doses

Dogs, Cats, Horses, Rabbits, Guinea pigs, Chinchillas, Sugar gliders and Primates

General dose range

25–50 mg/kg PO q12–24h with a fatty meal — check the species tables for the indication

Routes

PO

Last reviewed

1 October 2026

Indications

• Dermatophytosis (ringworm) — Microsporum canis, Trichophyton spp.
• Refractory or generalised dermatophyte infections requiring systemic therapy
• Dermatophytosis in horses (with topical therapy/environmental control)

Griseofulvin 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

• Dermatophytosis: MICROSIZE doses (ultramicrosize 5–10 mg/kg once daily; Papich ultramicrosize 30 mg/kg/day divided). Papich 5e: 25 mg/kg q12h PO, up to 50–60 mg/kg q12h in refractory cases. Plumb’s p.596: 25 mg/kg q12h for 42–56 days; 50 mg/kg once daily (Frank). Give after a fatty meal; teratogenic.

Cats

• Dermatophytosis (ringworm): MICROSIZE doses (ultramicrosize: 5–10 mg/kg once daily). Papich 5e: 25 mg/kg q12h PO. Plumb’s p.596: 50 mg/kg once daily or 25 mg/kg q12h for 42–70 days (Greene); 50–120 mg/kg/day divided (Foil). Give with a fatty meal; continue 2 weeks past cure and 2–3 negative cultures. Test FIV status first (marrow suppression); teratogenic.

Horses

• Dermatophytosis (ringworm): Papich 5e: microsize powder 5.6 mg/kg q24h in feed for at least 10 days. Plumb’s p.596 (Davis 2008): microsize 5 mg/kg PO once daily (halve for ultramicrosize); smaller doses for foals/ponies. Contraindicated in pregnant mares (teratogenic).

Rabbits

• Dermatophytosis: Plumb’s p.596 (Ivey & Morrisey 2000): microsize 25 mg/kg PO q12–24h for a month; ultramicrosize 6.25 mg/kg q12h for 4–6 weeks.

Guinea pigs

• Dermatophytosis: Plumb’s p.596: 25 mg/kg PO once daily for 14–28 days (Adamcak & Otten; Johnson 2006).

Chinchillas

• Dermatophytosis: Plumb’s p.596: 25 mg/kg PO once daily for 30–60 days (Hayes 2000; Johnson 2006).

Sugar gliders

• Dermatophytosis: Carpenter Exotic Animal Formulary 6th ed, Table 7-1 (p.497): sugar gliders 20 mg/kg PO q24h ×30–60 days. Fungistatic; rarely used now that safer options exist. Teratogenic — avoid in pregnancy.

Primates

• Dermatophytosis (monkeys, marmosets): Carpenter Exotic Animal Formulary 6th ed, Table 13-2 (p.684): monkeys 20 mg/kg PO q24h; common marmosets 25 mg/kg PO q24h ×30–60 days for dermatophytosis. Teratogenic — avoid in pregnancy.

Contraindications

PREGNANCY — absolute (teratogenic; do not handle if pregnant). FIV-positive cats (severe neutropenia/pancytopenia risk). Pre-existing bone-marrow suppression or hepatic disease. Known hypersensitivity. Porphyria. Not effective against yeasts/Malassezia or systemic mycoses.

Species-specific warnings

Cats: Test FIV status first — FIV-positive cats can develop fatal neutropenia/pancytopenia. Monitor CBC throughout; itraconazole is a safer alternative.

Adverse effects

• GI upset (vomiting, diarrhoea, anorexia)
• Bone-marrow suppression (neutropenia, pancytopenia) — idiosyncratic, severe in FIV+ cats
• Hepatotoxicity
• Teratogenicity (fetal malformations)
• Ataxia/CNS signs, photosensitivity (occasional)

Drug interactions

• Hepatic enzyme inducer: reduces efficacy of warfarin, ciclosporin, phenobarbital, oral progestins (and is itself induced)
• Phenobarbital: reduces griseofulvin absorption/levels
• Alcohol: disulfiram-like reaction (formulations)
• Fatty food: markedly increases absorption (give with fat)

Pregnancy and lactation

CONTRAINDICATED — teratogenic (skeletal/CNS fetal malformations). Pregnant women should not handle the drug; do not use in pregnant animals.

Monitoring

• CBC regularly (every 1–2 weeks) — neutropenia/pancytopenia, especially in cats
• FIV status BEFORE starting in cats
• Liver enzymes
• Dermatophyte cultures to define endpoint (treat to ≥2 negatives); confirm patient not pregnant

Toxicity and overdose

Beyond GI upset, the serious toxicities are idiosyncratic BONE-MARROW SUPPRESSION (neutropenia/pancytopenia — disproportionately in FIV-positive cats), hepatotoxicity, and teratogenicity. CNS signs (ataxia) and photosensitivity occur occasionally. These risks, plus newer safer azoles, have reduced its use.

Management: No specific antidote. Discontinue; supportive care, monitor CBC (marrow suppression) and liver values; manage neutropenia (antibiotic cover, possibly G-CSF) and hepatotoxicity supportively. Decontaminate large recent ingestions.

Clinical pearls

• A keratin-targeting ringworm drug — it only works as new, treated keratin grows in, so treat for weeks to NEGATIVE CULTURES, not just clinical improvement
• Always give with a FATTY meal (absorption is otherwise poor)
• Two hard rules: NEVER in pregnancy (teratogen) and check FIV status in cats (fatal marrow suppression risk) — monitor CBC
• Itraconazole/terbinafine are now often preferred (safer) for dermatophytosis — reserve griseofulvin accordingly
• Combine systemic therapy with topical antifungals and rigorous environmental decontamination

Mechanism of action

Griseofulvin binds fungal microtubules and disrupts mitotic spindle formation, inhibiting fungal cell division (fungistatic against dermatophytes). It is incorporated into newly forming keratin, making it resistant to dermatophyte invasion — so cure requires growth of new, drug-laden keratin to replace the infected tissue, hence the long treatment duration. Its absorption is greatly enhanced by dietary fat.

Formulations and products

• 125 mg tablet (microsize)
• 250 / 500 mg tablet
• Oral suspension
• Grisovin — 125 / 250 / 500 mg tablet, Tablet (human-label)
• Fulcin / Griseofulvin — 125 / 250 mg tablet, Tablet (human-label)

Storage

Tablets/suspension: 15–30 °C, dry, 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

• Caspofungin
• Clotrimazole
• Enilconazole
• Fluconazole
• Itraconazole
• Ketoconazole
• Lime Sulfur (Lime Sulphur Dip)
• Miconazole

Frequently asked questions