What is the recommended dosage and treatment duration of Terbinafine (antifungal medication) for fungal infections?

Terbinafine Dosage and Treatment Duration for Fungal Infections

For fungal nail infections (onychomycosis), terbinafine should be administered as 250 mg once daily for 6 weeks for fingernail infections and 12 weeks for toenail infections. 1

Dosage Recommendations 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, 2

Tinea Capitis (Scalp Ringworm)

• Weight-based dosing:
  • <20 kg: 62.5 mg daily for 2-4 weeks 2
  • 20-40 kg: 125 mg daily for 2-4 weeks 2

  • 40 kg: 250 mg daily for 2-4 weeks 2

Other Dermatophyte Infections

• Tinea pedis (athlete's foot): 250 mg once daily for 2-6 weeks 2, 3
• Tinea corporis/cruris (body/groin ringworm): 250 mg once daily for 2-4 weeks 2, 3

Mechanism of Action and Efficacy

Terbinafine is an allylamine antifungal that works by inhibiting squalene epoxidase, blocking ergosterol synthesis in the fungal cell wall 4. This creates both:

• Depletion of ergosterol (fungistatic effect)
• Accumulation of squalene (fungicidal effect) 4

Terbinafine demonstrates:

• Fungicidal activity against dermatophytes with very low minimum inhibitory concentration (MIC) of approximately 0.004 μg/mL 4
• Superior efficacy against Trichophyton species compared to other antifungals 2
• Mycological cure rates of 73-94% for toenail infections 2, 5

Advantages Over Other Antifungals

Terbinafine offers several advantages over other antifungal medications:

• Higher efficacy: More effective than griseofulvin for dermatophyte infections 3
• Shorter treatment duration: Compared to griseofulvin which requires 12-18 months for toenail infections 2
• Better safety profile: Fewer drug interactions than itraconazole 4, 2
• Fungicidal action: Unlike many azoles which are only fungistatic 3, 6

Safety Considerations and Monitoring

Before Starting Treatment

• Baseline liver function tests (ALT and AST) are recommended 1
• Assess for contraindications:
  • History of allergic reaction to terbinafine 1
  • Severe hepatic impairment 2, 1

Common Side Effects

• Headache, diarrhea, rash, dyspepsia, pruritus
• Taste disturbance (occurs in approximately 1:400 patients) 4, 1

Serious Adverse Effects to Monitor

• Liver problems that could lead to transplant or death
• Taste or smell disturbance (may be prolonged or permanent)
• Depressive symptoms
• Severe neutropenia
• Serious skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis) 1

Drug Interactions

Terbinafine is an inhibitor of CYP450 2D6 and may interact with:

• Desipramine
• Cimetidine (increases terbinafine plasma concentration)
• Rifampin (decreases terbinafine plasma concentration)
• Cyclosporine
• Fluconazole
• Caffeine 1

Treatment Failure Considerations

If treatment fails, consider:

• Poor compliance
• Poor absorption
• Relative insensitivity of the organism
• Reinfection
• Immunosuppression
• Dermatophyte resistance
• Subungual dermatophytoma 2

Special Populations

Pediatric Patients

• Terbinafine has shown efficacy and safety in children with tinea capitis and onychomycosis 7
• Weight-based dosing should be used as outlined above 2

Diabetic Patients

• Terbinafine is preferred due to lower risk of drug interactions 2

Immunosuppressed Patients

• Terbinafine or fluconazole is preferred over itraconazole due to fewer interactions with antiretrovirals 2

Terbinafine's lipophilic and keratophilic properties allow it to persist in the stratum corneum, nails, and hair for months after discontinuation, contributing to its high efficacy in treating fungal infections 6.