🌿 Terbinafine (Lamisil) in Veterinary Dermatology 2025 — by Dr Duncan Houston

Revised February 20, 2025 • No dosing info online • Requires vet supervision

1. Introduction to Terbinafine

Terbinafine, widely known as Lamisil, is a potent ally in treating fungal skin infections like dermatophytosis (ringworm) in pets. First used in humans, it’s now a trusted veterinary option for cats and dogs.

• 🧱 Targets fungal cell walls without harming host cells
• 💊 Available as tablets, granules, and 1% topical gel
• 🐾 Ideal for skin/fur infections, with other emerging uses

2. Mechanism of Action

Fungal cells contain ergosterol in their membranes, critical for survival. Terbinafine blocks the enzyme squalene epoxidase, disrupting ergosterol synthesis. This leads to toxic buildup of squalene and fungal wall collapse—without affecting human or animal cells.

3. Indications: When and Why It's Used

1. **Ringworm (dermatophytosis)** – Most common use in pets
2. **Other fungal conditions** – e.g., Aspergillus infections
3. **Potential off-label applications** – severe fungal otitis, systemic fungal issues (under study)

4. Formulations & Administration

Best given with food for absorption. Avoid light exposure; store at room temperature.

5. Treatment Protocols

Typical dosing is 1–3× per day for 4–8 weeks, depending on infection severity and species. Treatment duration extends until cultures or Wood’s lamp exams confirm fungal clearance.

• 🐶 Dogs: often twice daily
• 🐱 Cats: once or twice daily
• Topical gel applied 1–2× per day on isolated lesions

6. Side Effects & Safety

6.1 Common Side Effects

• 🤢 Upset stomach—nausea, occasional vomiting
• 💨 Dogs may pant temporarily
• 👀 Conjunctivitis or mild eye irritation possible

6.2 Serious Concerns

Rare but important: liver toxicity, skin reactions, bone marrow suppression—primarily reported in humans. Avoid use in pets with known liver or kidney issues.

7. Drug Interactions

Terbinafine uses liver enzymes for metabolism, so it can affect levels of other medications:

• ↑ levels: selegiline, amitraz, beta-blockers, TCAs, SSRIs, narcotics
• ↓ levels: cyclosporine efficacy is reduced
• Cimetidine slows terbinafine metabolism

8. Special Precautions

• ⛔ Avoid with liver or kidney disease
• 👶 Not for pregnant or lactating animals
• No double-dosing if a dose is missed; resume normally

9. Monitoring During Treatment

Periodic checks are strongly advised:

• ✅ Look for GI signs or lethargy
• 🔬 Run liver enzyme panels every 2–4 weeks
• 🐾 Monitor ocular health if topical gel used near eyes

10. Comparison with Azole Antifungals

11. Case Examples

12. Client Communication Tips

• 🗣️ Explain fungal life cycle & need for long treatment
• 🙌 Emphasize giving with meals and avoiding missed doses
• 🧪 Recommend environmental cleaning to prevent reinfection
• 📞 Encourage reporting GI symptoms or lethargy promptly

13. Ongoing & Future Research

• Investigating oral terbinafine for systemic fungal disease in pets
• Combination protocols with azoles to reduce resistance
• Lower-dose regimens to minimize side effects

14. Regulatory Status

Though Lamisil is human-labeled, its use in veterinary patients is off-label but common under vet discretion and informed client consent.

15. Conclusion

Terbinafine is a powerful, targeted treatment for fungal skin infections in pets. With thoughtful monitoring and client education, it delivers effective results with minimal side effects. For systemic cases or resistant strains, additional diagnostics or combined therapy may be needed. — Dr Duncan Houston 🐾