Terbinafine
Terbinafine is an allylamine antifungal used mainly against dermatophyte infections in veterinary patients. Its tissue distribution and keratin affinity support use in skin and hair infections. Selected deeper fungal or fungus-like infections have also been treated in combination protocols, but the evidence and expected response vary substantially by organism and infection site.
Group
Allylamine antifungal
Mechanism of Action
Terbinafine inhibits fungal squalene epoxidase, an early enzyme in ergosterol synthesis. Reduced ergosterol disrupts membrane function, while accumulated squalene can become toxic to fungal cells. This produces fungicidal activity against many susceptible dermatophytes. Differences in sterol metabolism and drug exposure contribute to variation in susceptibility among other organisms.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 30–40 mg/kg | PO | Every 24 h | Up to 21 days; Give with food; reported course 2-3 weeks. |
| Malassezia dermatitis | 30 mg/kg | PO | Every 24 h | Partially effective in reported use; at least 3 weeks. |
| Intermittent Malassezia treatment | Reference only | PO | 30 mg/kg orally twice weekly for at least 3 weeks was partially effective; a twice-weekly calendar schedule is not a fixed daily interval. | |
| Dermatophytosis | 10–20 mg/kg | PO | Every 24 h | |
| Dermatophytosis | 25 mg/kg | PO | Every 24 h | |
| Nasal aspergillosis adjunct | 5–10 mg/kg | PO | Every 12 h | Reported 3-6 months with local therapy when cribriform involvement complicates treatment. |
| Pythiosis combination adjunct | 10 mg/kg | PO | Every 24 h | With itraconazole 10 mg/kg orally twice daily when advanced disease precludes complete excision. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Dermatophytosis | 30–40 mg/kg | PO | Every 24 h | At least 2 weeks; minimum duration is not a maximum cap. |
| Size-based dermatophyte treatment | Reference only | PO | Reported gives 62.5 mg for small, 125 mg for medium and 250 mg for large cats once daily, but numeric size boundaries are not supplied. | |
| Dermatophytosis | 10–20 mg/kg | PO | Every 24 h | |
| Dermatophytosis | 25 mg/kg | PO | Every 24 h | |
| Pulse dermatophytosis treatment | 20 mg/kg | PO | Every 24 h | Up to 7 days; Seven days on followed by 21 days off; retain the off-period when planning repeated pulses. |
| Dermatophyte mycetoma case series | 26–31 mg/kg | PO | Every 24 h | Two cats treated 12-14 weeks; case-series experience, not a universally established course. |
| Nasal aspergillosis adjunct | 5–10 mg/kg | PO | Every 12 h | Reported 3-6 months with local therapy when cribriform involvement complicates treatment. |
| Pythiosis combination adjunct | 10 mg/kg | PO | Every 24 h | With itraconazole 10 mg/kg orally twice daily when advanced disease precludes complete excision. |
| Azole-resistant cryptococcosis | 10 mg/kg | PO | Every 24 h | CNS disease may need prolonged or lifelong therapy. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Reported antifungal treatment | 30 mg/kg | PO | Every 12 h | Clinical efficacy in horses is not established. |
Birds
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Mycotic infection | 10–15 mg/kg | PO | Every 12–24 h | |
| Aspergillosis | 10–15 mg/kg | PO | Every 12 h | Up to 28 days |
Indications
- Treatment of dermatophytosis in dogs and cats with a supported regimen.
- Treatment of selected susceptible dermatophyte infections in birds or other exotic patients.
- Treatment of selected Malassezia dermatitis in dogs, with variable clinical response.
- Specialist adjunctive treatment of selected aspergillosis or other deeper mycoses.
- Selected combination treatment of pythiosis or refractory cryptococcosis, with limited disease-specific clinical evidence.
Contraindications
- Hepatic abnormalities warrant assessment.
Adverse effects
- Vomiting, anorexia, liver enzyme elevation and feline facial pruritus; crushed tablets in molasses irritated equine oral mucosa.
Toxicity
Veterinary overdose information is limited; assess GI, hepatic and neurologic signs and treat supportively.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Terbinafine 250 mg | Tablet | 250 mg / tablet | PO |
Monitoring and Administration
Give canine oral doses with food and assess fungal response; efficacy is variable. Reported Ora-Sweet suspension stability is 42 days.
Avian nebulization reports use 1 mg/mL solution, sometimes with acetylcysteine, but do not give a patient-specific delivered amount or full session schedule. Lagendiosis combination in one dog used terbinafine 5-10 mg/kg orally daily, itraconazole 10 mg/kg daily and repeated aggressive surgery; retain as case-specific evidence.