Terbinafine is an allylamine antifungal medication considered first-line treatment for dermatophytosis (ringworm) in dogs and cats, alongside itraconazole. Sold under the human brand name Lamisil, terbinafine works through a different mechanism than azole antifungals (itraconazole, ketoconazole), which gives it a significant practical advantage: fewer drug interactions. This makes terbinafine particularly useful for pets already on other medications. The oral form requires a veterinary prescription, while topical terbinafine cream (Lamisil AT) is available over the counter, though oral treatment is strongly preferred for pets with dermatophytosis.
What Is Terbinafine Used For?
Terbinafine is prescribed primarily for fungal skin infections:
- Dermatophytosis (ringworm) — caused by Microsporum canis, Microsporum gypseum, and Trichophyton mentagrophytes in dogs and cats
- Onychomycosis (fungal nail infections) — off-label
- Malassezia dermatitis — off-label, though azole antifungals are typically preferred
Ringworm is the most common fungal infection in dogs and cats, and it is zoonotic (can spread to humans). Treatment typically requires 4-8 weeks of oral antifungal therapy combined with topical treatment and environmental decontamination.
How Does Terbinafine Work?
Terbinafine inhibits the enzyme squalene epoxidase, which is essential for the synthesis of ergosterol — a critical component of fungal cell membranes. Without ergosterol, the fungal cell membrane becomes unstable, leading to cell death. This mechanism is fungicidal (directly kills fungi) at therapeutic concentrations, unlike azole antifungals which are primarily fungistatic (stop fungal growth).
Terbinafine has excellent affinity for keratinized tissues (skin, hair, nails), where dermatophytes live. It concentrates in the stratum corneum and hair follicles, achieving high local concentrations at the site of infection. It remains in the skin for weeks after discontinuation, providing a sustained antifungal effect.
Dosage
Your veterinarian will determine the exact dose and duration.
Dogs
| Dog’s Weight | Typical Dose | Frequency | Duration |
|---|---|---|---|
| 10 lbs (4.5 kg) | 30-60 mg | Once daily | 4-6 weeks |
| 25 lbs (11.3 kg) | 60-125 mg | Once daily | 4-6 weeks |
| 50 lbs (22.7 kg) | 125-250 mg | Once daily | 4-6 weeks |
| 75+ lbs (34+ kg) | 250-500 mg | Once daily | 4-6 weeks |
Standard canine dose: 5-10 mg/kg once daily (some references use 30-40 mg/kg for dermatophytosis).
Cats
| Cat’s Weight | Typical Dose | Frequency | Duration |
|---|---|---|---|
| 6-12 lbs (2.7-5.4 kg) | 30-40 mg/kg (per tablet) | Once daily or per protocol | 4-8 weeks |
Standard feline dose: 30-40 mg/kg once daily. Some veterinary dermatologists use pulse dosing (1 week on, 1 week off).
Treatment duration is guided by fungal cultures — treatment continues until at least one negative fungal culture is obtained, typically 4-8 weeks minimum.
How to Give Terbinafine to Your Dog or Cat
- Available as tablets (250 mg) and oral granules.
- Can be given with or without food. Giving with food may improve absorption.
- Topical terbinafine cream (Lamisil AT, OTC) is not sufficient as sole treatment for pets — oral treatment is necessary to eliminate dermatophyte infections from hair follicles. Topical treatment may be used as an adjunct.
- Treatment is guided by fungal cultures (dermatophyte test medium/DTM or PCR). Do not stop treatment based solely on resolution of clinical signs — continue until cultures are negative.
- Environmental decontamination is important to prevent reinfection: wash bedding, vacuum thoroughly, and use antifungal environmental sprays.
Side Effects
| Common Side Effects | Serious Side Effects (Contact Your Vet) |
|---|---|
| Mild GI upset (vomiting, diarrhea) | Hepatotoxicity (elevated liver enzymes, jaundice) |
| Decreased appetite | Persistent vomiting |
| Skin reactions | |
| Significant lethargy |
Terbinafine is generally well-tolerated in both dogs and cats. Liver enzyme monitoring is recommended during prolonged treatment courses.
Drug Interactions
- Terbinafine has significantly fewer drug interactions than azole antifungals (itraconazole, ketoconazole) because it does not significantly inhibit the cytochrome P450 3A4 enzyme.
- Cimetidine: May increase terbinafine levels.
- Rifampin: May decrease terbinafine levels.
- Cyclosporine: Minimal interaction compared to azole antifungals.
Contraindications
- Known hypersensitivity to terbinafine
- Severe liver disease — terbinafine is hepatically metabolized
- Pregnant or lactating animals — safety not established
- Use with caution in animals with pre-existing liver problems
Storage
- Store at controlled room temperature, 68-77degF (20-25degC).
- Protect from light and moisture.
- Keep in original container.
- Keep out of reach of children and pets.
Cost & Availability
Terbinafine is available as a generic human medication at affordable cost.
- Approximate cost: $15-$30 per month for most dogs and cats
- Available forms: 250 mg tablets (oral); topical cream 1% (OTC, Lamisil AT)
- Can be filled at human pharmacies with a veterinary prescription (oral form)
- Topical cream available OTC at pharmacies and drugstores
Frequently Asked Questions
How long does ringworm treatment take? Typically 4-8 weeks of oral antifungal therapy, though some cases require longer treatment. The definitive endpoint is a negative fungal culture, not just resolution of visible lesions. Stopping treatment too early is a common cause of relapse.
Is terbinafine better than itraconazole for ringworm? Both are considered first-line treatments. Terbinafine has the advantage of being fungicidal (kills fungi directly) and having fewer drug interactions. Itraconazole may be preferred in some cases based on the specific dermatophyte species and the individual animal’s medication profile. Your veterinary dermatologist can advise on the best choice.
Can I use Lamisil cream on my dog or cat? Topical terbinafine cream alone is not sufficient to treat ringworm in pets because the infection extends into hair follicles where topical agents cannot reach effectively. Oral treatment is necessary. Topical treatment may be used as an adjunct to reduce environmental contamination.
Is ringworm contagious to humans? Yes. Dermatophytosis is zoonotic and can spread from pets to humans (and vice versa). While your pet is being treated, practice good hygiene: wash hands after handling your pet, clean shared surfaces, and consult your physician if you develop circular, itchy skin lesions.
Sources & References
- Merck Veterinary Manual - Dermatophytosis
- VCA Hospitals - Ringworm in Dogs and Cats
- PetMD - Terbinafine for Dogs and Cats
- Plumb’s Veterinary Drug Handbook - Terbinafine
- dvm360 - Dermatophytosis Treatment Guidelines
Verification Notes
Terbinafine’s description as an “Allylamine antifungal. First-line (with itraconazole) for ringworm. Different mechanism than azoles — fewer drug interactions. Well-tolerated in dogs and cats. Oral form is Rx; topical cream is OTC but oral treatment is preferred for pets.” is directly confirmed by the research corpus.