Griseofulvin
Griseofulvin is an orally administered antifungal used against dermatophyte infections of keratinized tissues. It is deposited in newly forming skin, hair and claws, which supports its role in ringworm treatment. Veterinary applications include dogs, cats and selected other species, although use has declined as other systemic antifungals have become more widely available.
Group
Systemic dermatophyte antifungal
Mechanism of Action
Griseofulvin disrupts fungal microtubule function and formation of the mitotic spindle, inhibiting fungal cell division. Incorporation into developing keratin makes newly produced skin and hair less susceptible to invasion by dermatophytes. Resolution develops as infected keratin is shed and replaced by protected tissue, so its clinical effect follows tissue turnover as well as suppression of fungal growth.
Dose Rates
Dog
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis (microsize) — Initial | 25 mg/kg | PO | Every 12 h | Do not use in: Pregnancy in cats |
| Dermatophytosis (microsize) — Maintenance | 50–60 mg/kg | PO | Every 12 h | Do not use in: Pregnancy in cats; Refractory cases after reassessment. |
| Dermatophytosis (ultramicrosize) | Reference only | PO | Do not use in: Pregnancy in cats; 30 mg/kg total per day in divided administrations; division schedule is not specified. Do not treat the total daily amount as a single repeated dose. |
Cat
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis (microsize) | 25 mg/kg | PO | Every 12 h | Do not use in: Pregnancy in cats |
| Eosinophilic granuloma complex | 25 mg/kg | PO | Every 12 h | Microsize formulation with food; assess response after at least one month. Monitor for marrow suppression. |
Horse
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis (microsize) | 5.6 mg/kg | PO | Every 24 h | Do not use in: Pregnancy in cats; Microsize powder mixed with feed; minimum 10-day course. |
Gerbil
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 25 mg/kg | PO | Every 24 h | Up to 28 days; Microsize formulation; duration depends on clinical and culture response. |
Guinea Pig
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 25 mg/kg | PO | Every 24 h | Up to 28 days; Microsize formulation; duration depends on clinical and culture response. |
Hamster
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 25 mg/kg | PO | Every 24 h | Up to 28 days; Microsize formulation; duration depends on clinical and culture response. |
Rat
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 25 mg/kg | PO | Every 24 h | Up to 28 days; Microsize formulation; duration depends on clinical and culture response. |
Mouse
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 25 mg/kg | PO | Every 24 h | Up to 14 days; Microsize formulation; duration depends on clinical and culture response. |
Chinchilla
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 25 mg/kg | PO | Every 24 h | Up to 60 days; Microsize formulation; duration depends on clinical and culture response. |
Rabbit
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 25 mg/kg | PO | Every 12–24 h | Up to 30 days; Microsize formulation. |
| Ultramicrosize dermatophytosis treatment | Reference only | PO | 6.25 mg/kg every 12 hours for 4–6 weeks using ultramicrosize griseofulvin. This formulation must not be automatically substituted for the microsize preparation. |
Pig
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 20 mg/kg | PO | Every 24 h | Up to 42 days; Microsize formulation; food-animal residue requirements are product- and jurisdiction-specific. |
Ratite
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 35–50 mg/kg | PO | Every 24 h | Microsize formulation. |
Indications
- Systemic treatment of dermatophytosis affecting skin, hair or claws in dogs and cats, including susceptible Microsporum and Trichophyton infections.
- Treatment of selected equine ringworm infections, including susceptible Trichophyton equinum or Microsporum infections.
- Treatment of selected dermatophyte infections in other veterinary species where an appropriate regimen is supported.
Contraindications
- Pregnant cats
- Use cautiously in FIV-positive cats or those with marrow disease.
Interactions
- Induces drug-metabolizing enzymes and may lower other drug exposures.
Adverse effects
- Anemia, leukopenia or pancytopenia
- Vomiting, diarrhea, anorexia and depression
- Teratogenicity
Toxicity
Potentially irreversible idiosyncratic pancytopenia has been reported in cats.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Griseofulvin microsize 125 mg Microsize formulation; do not substitute for ultramicrosize by equal milligrams. | Tablet | 125 mg / tablet | PO |
| Griseofulvin microsize 250 mg Microsize formulation; do not substitute for ultramicrosize by equal milligrams. | Tablet | 250 mg / tablet | PO |
| Griseofulvin microsize 500 mg Microsize formulation; do not substitute for ultramicrosize by equal milligrams. | Tablet | 500 mg / tablet | PO |
| Griseofulvin microsize suspension 25 mg/mL Microsize formulation; do not substitute for ultramicrosize by equal milligrams. | Oral Liquid | 25 mg / mL | PO |
| Griseofulvin microsize powder 2500 mg/15 g Microsize formulation; do not substitute for ultramicrosize by equal milligrams. | Powder | 2500 mg / 15 g | PO |
| Griseofulvin ultramicrosize 125 mg Distinct bioavailability; use ultramicrosize-specific dosing, not a microsize regimen. | Tablet | 125 mg / tablet | PO |
| Griseofulvin ultramicrosize 250 mg Distinct bioavailability; use ultramicrosize-specific dosing, not a microsize regimen. | Tablet | 250 mg / tablet | PO |
Monitoring and Administration
Monitor CBC. Give with a fatty meal to improve absorption; shake suspension.
Microsize and ultramicrosize formulations have different exposure and dosing. Do not substitute at the same amount.
Small-animal treatment often needs at least 4 weeks and sometimes several months, guided by resolution and fungal testing.