What are the uses and dosage of Terbinafine (antifungal medication)?

Terbinafine Uses and Dosage

Terbinafine is primarily indicated for the treatment of onychomycosis (fungal nail infections) with a standard oral dosage of 250 mg once daily for 6 weeks for fingernail infections and 12 weeks for toenail infections. 1

Indications

Terbinafine is an allylamine antifungal medication with the following approved uses:

• Primary indication: Treatment of onychomycosis (fungal nail infections) due to dermatophytes 1
• Mechanism of action: Inhibits squalene epoxidase, essential for ergosterol biosynthesis in the fungal cell wall, resulting in both fungistatic and fungicidal effects 2
• Spectrum of activity:
  • Fungicidal against dermatophytes (particularly T. rubrum and T. mentagrophytes)
  • Less effective against Candida species compared to azole antifungals 2

Dosage Regimens

Adult Dosing

• Fingernail onychomycosis: 250 mg once daily for 6 weeks 1
• Toenail onychomycosis: 250 mg once daily for 12-16 weeks 2
• Administration: Can be taken with or without food 1

Pediatric Dosing

• For dermatophyte infections in children (weight-based dosing):
  • Under 20 kg: 62.5 mg/day 3
  • 20-40 kg: 125 mg/day 3
  • Over 40 kg: 250 mg/day (adult dose) 3
• Duration for tinea capitis: 2-4 weeks for Trichophyton species 3

Pharmacokinetics

• Absorption: Rapid (>70%), reaching peak plasma concentration within 2 hours 4
• Bioavailability: 70-80% 4
• Protein binding: >90% 4
• Distribution: Highly lipophilic and keratophilic, distributes well into skin and nails 2
• Persistence: Detected in nail within 1 week of starting therapy and persists for up to 6 months after treatment completion 2
• Elimination: Primarily renal clearance 2

Monitoring and Safety Considerations

Baseline Testing

• Liver function tests and complete blood count recommended for patients with:
  • History of heavy alcohol consumption
  • Hepatitis
  • Hematological abnormalities 2

Contraindications

• Active or chronic liver disease 2
• History of allergic reaction to oral terbinafine 1

Common Side Effects

• Gastrointestinal: Nausea, diarrhea, dyspepsia, abdominal pain, flatulence (49% of reported side effects) 2, 1
• Dermatological: Rash, pruritus, urticaria, eczema (23% of reported side effects) 2
• Sensory: Taste disturbance or loss (may be prolonged or permanent) 1

Serious Adverse Effects

• Hepatotoxicity: Rare but serious, can lead to liver transplant or death 1
• Severe skin reactions: Stevens-Johnson syndrome, toxic epidermal necrolysis 2, 1
• Neutropenia: Discontinue if neutrophil count ≤1,000 cells/mm³ 1
• Smell disturbance: May be prolonged or permanent 1
• Lupus erythematosus: New onset or worsening 1

Drug Interactions

• CYP450 2D6 inhibition: May interact with medications metabolized by this enzyme 2, 1
• Notable interactions with:
  • Desipramine
  • Cimetidine
  • Fluconazole
  • Cyclosporine
  • Rifampin
  • Caffeine 1

Clinical Efficacy

• Mycological cure rates: 73-94% for dermatophyte onychomycosis 3
• Comparative efficacy: More effective than griseofulvin and continuous or intermittent itraconazole in dermatophyte onychomycosis 5, 6
• Treatment outcomes: Clinical cure rates continue to improve after treatment cessation due to fungicidal mechanism and residual effect 5

Special Considerations

• Pregnancy: Should not be started during pregnancy without consulting a physician 1
• Breastfeeding: Passes into breast milk; discuss risks with physician 1
• Missed doses: Take as soon as remembered unless within 4 hours of next scheduled dose 1
• Men planning conception: Manufacturers caution against fathering a child for 6 months after therapy 2

Terbinafine represents the first-line treatment for dermatophyte onychomycosis due to its high efficacy, favorable safety profile, and relatively low potential for drug interactions compared to alternatives.