Terbinafine Dosage and Treatment Duration for Fungal Infections
For fungal nail infections (onychomycosis), terbinafine should be administered at 250 mg once daily for 6 weeks for fingernails and 12 weeks for toenails, as this regimen provides the highest cure rates with minimal side effects. 1
Recommended Dosages by Infection Type
Onychomycosis (Nail Infections)
- Fingernail infections: 250 mg once daily for 6 weeks 1
- Toenail infections: 250 mg once daily for 12 weeks 1
- Mycological cure rates range from 73-94% for toenails 2
- Clinical studies show 82% mycological cure for toenail infections after 12 weeks of treatment 3
Tinea Capitis (Scalp Ringworm)
- Weight-based dosing 2:
- <20 kg: 62.5 mg daily for 2-4 weeks
- 20-40 kg: 125 mg daily for 2-4 weeks
40 kg: 250 mg daily for 2-4 weeks
- More effective against Trichophyton species than Microsporum species 2
Other Dermatophyte Infections
- Tinea corporis/cruris: 250 mg once daily for 2-4 weeks 4
- Tinea pedis: 250 mg once daily for 2-4 weeks 4
Administration Considerations
- Can be taken with or without food 1
- If a dose is missed, take as soon as remembered unless less than 4 hours before next dose 1
- Terbinafine is highly lipophilic and keratophilic, allowing it to persist in nails, skin, and hair for months after treatment cessation 5
Alternative Dosing Regimens
Some studies have explored pulse therapy options:
- Weekly intermittent dosing: 500 mg/day for 1 week per month for 4 months 5
- Single-dose: 1000 mg per month for 4 months 5
- A comparative study showed that pulsed dosing (500 mg/day for 1 week every 4 weeks over 16 weeks) achieved similar mycological cure rates to continuous dosing (250 mg/day for 16 weeks) 6
Mechanism of Action and Efficacy
Terbinafine is an allylamine antifungal that:
- Inhibits squalene epoxidase, blocking ergosterol synthesis in the fungal cell wall 7
- Has fungicidal activity against dermatophytes, with very low minimum inhibitory concentration (0.004 μg/mL) 7
- Is more effective than itraconazole and griseofulvin for dermatophyte infections 7, 4
- Achieves mycological cure in >80% of patients with superficial dermatophyte infections 4
Safety and Monitoring
- Baseline liver function tests are recommended before starting treatment 2
- Common side effects include headache, diarrhea, rash, dyspepsia, liver enzyme abnormalities, and taste disturbance 1
- Serious but rare side effects include liver failure, severe taste/smell disturbance, depressive symptoms, and severe skin reactions 1
- Contraindicated in patients with history of allergic reaction to oral terbinafine 1
Drug Interactions
- Terbinafine inhibits CYP2D6 and may affect metabolism of:
Special Populations
- Children: Terbinafine is effective and safe for tinea capitis and onychomycosis in children, with weight-based dosing 8
- Hepatic impairment: Avoid in severe hepatic disease 2
- Pregnancy: Not recommended without consulting physician 1
Treatment Failure Considerations
If treatment fails, consider:
- Poor compliance
- Poor absorption
- Relative insensitivity of the organism
- Reinfection 2
Terbinafine's fungicidal mechanism of action and residual effect in tissue often lead to improved mycological cure rates even after treatment cessation 4.