What is the recommended treatment and dosage for Terbinafine (Lamisil) in fungal infections?

Terbinafine Treatment for Fungal Infections

For dermatophyte onychomycosis (nail infections), terbinafine 250 mg daily is the first-line treatment: 6 weeks for fingernails and 12 weeks for toenails, with superior efficacy compared to all other oral antifungals. 1, 2, 3

Dosing by Indication

Onychomycosis (Nail Infections)

• Toenail infections: 250 mg once daily for 12 weeks (can extend to 16 weeks for severe cases) 1, 2, 3
• Fingernail infections: 250 mg once daily for 6 weeks 3
• Re-evaluation timing: Assess response 3-6 months after treatment initiation, as clinical improvement continues after stopping therapy due to persistent nail concentrations 4, 2

Tinea Pedis (Foot Infections)

• 250 mg daily for 1-2 weeks achieves mycological cure rates of 80-90% 5
• Topical terbinafine 1% cream: Once daily for 1 week (significantly shorter than azoles which require 4 weeks) 6

Tinea Capitis (Scalp Ringworm) - Weight-Based Dosing

• < 20 kg: 62.5 mg daily for 2-4 weeks 4
• 20-40 kg: 125 mg daily for 2-4 weeks 4
• > 40 kg: 250 mg daily for 2-4 weeks 4

Tinea Corporis/Cruris (Body/Groin)

• 250 mg daily for 1-2 weeks for oral therapy 7
• Topical 1% cream: Once daily for 1 week 6

Why Terbinafine is Superior

Mechanism and Efficacy

• Truly fungicidal against dermatophytes (not just fungistatic like azoles), with extremely low minimum inhibitory concentration of 0.004 µg/mL 1
• Mycological cure rates approximately double those of itraconazole in the landmark L.I.ON. study: 76% vs 38% after 12 weeks, and 81% vs 49% after 16 weeks 8
• Long-term superiority: At 5-year follow-up, terbinafine showed complete cure rate of 35% vs 14% for itraconazole, with lower relapse rates (23% vs 53%) 8
• Persistent nail concentrations detected within 1 week of starting therapy and lasting at least 30 weeks after treatment completion 8

Comparative Evidence

• More effective than griseofulvin for all dermatophyte infections, with griseofulvin no longer recommended as first-line 1
• Superior to itraconazole for dermatophyte onychomycosis with Grade A-I evidence 1
• More effective than fluconazole in randomized trials 8

Important Limitations

When NOT to Use Terbinafine

• Candida infections: Terbinafine is only fungistatic (not fungicidal) against Candida species - use itraconazole or fluconazole instead 1
• Nondermatophyte moulds: Terbinafine shows lowest activity against Scopulariopsis, Fusarium, and Acremonium - itraconazole is preferred 1
• Mixed infections: If both dermatophytes and Candida are present, consider itraconazole for broader coverage 1

Safety Monitoring and Contraindications

Mandatory Pre-Treatment Testing

• Baseline liver function tests (ALT and AST) required before starting treatment 2, 3

Absolute Contraindications

• History of allergic reaction to oral terbinafine (risk of anaphylaxis) 3
• Active or chronic liver disease 1, 2
• Lupus erythematosus 1, 2

Enhanced Monitoring Required For:

• Pre-existing liver disease 2
• Concomitant hepatotoxic medications 2
• Continuous therapy > 1 month 2
• History of heavy alcohol consumption 2, 5

Critical Warnings

• Liver failure (potentially requiring transplant or causing death) has occurred - discontinue immediately if liver injury develops 3
• Taste disturbance occurs in 1:400 patients, can be severe, prolonged, or permanent - discontinue if this occurs 1, 3
• Smell disturbance including complete loss of smell may be prolonged or permanent - discontinue if this occurs 3
• Depressive symptoms have been reported - monitor for mood changes, feelings of worthlessness, or loss of interest 3
• Severe skin reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS syndrome - discontinue immediately if progressive rash develops 3
• Severe neutropenia - discontinue if neutrophil count ≤ 1,000 cells/mm³ 3

Drug Interactions

Minimal Interaction Profile

• Major advantage over azoles: Terbinafine has minimal drug interactions compared to itraconazole 1, 2
• Primary concern: Inhibits CYP450 2D6 isoenzyme 4, 2, 3

Specific Interactions

• Rifampin: Reduces terbinafine plasma concentrations 1, 3
• Cimetidine: Increases terbinafine plasma concentrations 1, 3
• Monitor closely: Desipramine, antihypertensives, cardiac medications, cyclosporine, caffeine 3

Common Adverse Effects

• Gastrointestinal: Most common (49% of reported side effects) - nausea, diarrhea, dyspepsia, abdominal pain, flatulence 5, 3
• Dermatological: 23% of reported side effects - rash, pruritus 5
• Overall incidence: Only 10.5% of patients experience adverse events in post-marketing surveillance 8
• Generally mild: Most effects are minor irritation or burning with topical formulations 9

Clinical Pearls

Treatment Success Factors

• Confirm diagnosis with microscopy or culture before starting treatment 3
• Patient counseling: Improvement continues after stopping therapy due to persistent drug levels in nails 8
• Preventive measures for tinea pedis: Thorough drying between toes, daily sock changes, periodic shoe cleaning 5

Cost-Effectiveness

• Despite higher upfront cost than griseofulvin, superior cure rates and lower relapse rates make terbinafine more cost-effective overall 1, 8
• Shorter treatment duration compared to griseofulvin (which requires 12+ months for toenails) improves compliance 1

Pregnancy and Breastfeeding

• Not recommended during pregnancy - discuss with physician before starting 3
• Passes into breast milk - consider alternative feeding methods 3