What is the recommended treatment and dosage for fungal infections using Terbinafine?

Terbinafine Treatment for Fungal Infections

For dermatophyte onychomycosis, prescribe terbinafine 250 mg once daily for 6 weeks for fingernail infections and 12 weeks for toenail infections, as this represents the gold standard with superior efficacy compared to other antifungals. 1, 2, 3, 4

Standard Adult Dosing by Infection Site

Toenail Onychomycosis

• 250 mg once daily for 12 weeks 1, 3, 4
• Re-evaluate 3-6 months after treatment initiation, as clinical improvement continues after therapy cessation due to terbinafine's persistence in nail tissue for up to 6 months 2, 3
• If disease persists at follow-up, additional treatment may be warranted 2

Fingernail Onychomycosis

• 250 mg once daily for 6 weeks 1, 3, 4
• This shorter duration is sufficient due to faster nail growth in fingers 5

Tinea Capitis (Scalp Ringworm)

• Weight-based dosing for 2-4 weeks: 6, 3
  • <20 kg: 62.5 mg daily
  • 20-40 kg: 125 mg daily

  • 40 kg: 250 mg daily

• Critical caveat: Terbinafine is highly effective against Trichophyton species but significantly less effective against Microsporum species; griseofulvin is superior for Microsporum infections 3

Pediatric Dosing for Onychomycosis

Weight-based daily dosing: 1, 3

• <20 kg: 62.5 mg daily
• 20-40 kg: 125 mg daily

• 40 kg: 250 mg daily (adult dose)

Treatment duration: 1

• Fingernails: 6 weeks
• Toenails: 12 weeks

Children demonstrate higher cure rates and faster response than adults, with one study showing 88% clinical cure in pediatric onychomycosis 1

Special Populations

Diabetic Patients

Terbinafine is the oral antifungal of choice for diabetics due to: 1

• Low risk of drug interactions
• No hypoglycemia risk
• Itraconazole is contraindicated in congestive heart failure (common in diabetics)
• Onychomycosis significantly predicts foot ulcer development in diabetes, making effective treatment critical for morbidity reduction 1

Immunosuppressed Patients (HIV/Transplant)

Terbinafine and fluconazole are preferred over azoles in immunosuppressed patients because: 1

• Minimal risk of interaction with antiretrovirals
• Itraconazole and ketoconazole have high interaction potential with antiretrovirals
• Most onychomycosis in immunosuppressed patients is due to T. rubrum, which responds well to terbinafine 1

Pre-Treatment Requirements and Monitoring

Baseline Testing

• Liver function tests (LFTs) are mandatory before initiating treatment 2, 3, 4
• Complete blood count (CBC) recommended, particularly in patients with history of hepatitis, heavy alcohol use, or hematological abnormalities 3

Enhanced Monitoring Indicated For:

• Pre-existing liver disease 2
• Concomitant hepatotoxic medications 2
• Continuous therapy exceeding one month 2
• History of heavy alcohol consumption 2

Absolute Contraindications

Do not prescribe terbinafine in: 2, 3, 4

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

Critical Safety Warnings

Hepatotoxicity

• Liver failure leading to transplant or death has occurred with oral terbinafine 4
• Discontinue immediately if liver injury develops 4

Severe Cutaneous Reactions

• Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported 3, 4
• Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome 4
• Discontinue immediately if signs of severe skin reaction occur 4

Sensory Disturbances

• Taste disturbance (including complete taste loss) can be severe, prolonged, or permanent 4
• Smell disturbance (including complete loss) may be prolonged or permanent 4
• Discontinue terbinafine if taste or smell disturbance occurs 4

Hematologic Toxicity

• Severe neutropenia has been reported 4
• Discontinue if neutrophil count ≤1,000 cells/mm³ 4

Psychiatric Effects

• Depressive symptoms have been reported with terbinafine use 4
• Monitor for development of depressive symptoms 4

Drug Interactions

Terbinafine has minimal drug interactions compared to azole antifungals, making it safer for patients on multiple medications 2, 3

Primary Interaction Concern

• Terbinafine inhibits cytochrome P450 2D6 isoenzyme 2, 3, 4
• Affects metabolism of: 4
  • Desipramine and other tricyclic antidepressants
  • Certain beta-blockers
  • Antiarrhythmics
  • Cimetidine
  • Fluconazole
  • Cyclosporine
  • Rifampin

Pharmacologic Rationale for Efficacy

• Terbinafine is fungicidal against dermatophytes with very low minimum inhibitory concentrations (approximately 0.004 μg/mL) 2, 6, 3
• Persists in nail tissue for 6 months after treatment completion due to long half-life and lipophilic properties 3
• This explains why mycological cure rates improve after treatment cessation 7
• Superior efficacy compared to itraconazole for dermatophyte onychomycosis 2, 6, 3

Common Adverse Events

Adverse events occurring in >2% of patients include: 4

• Headache
• Diarrhea
• Rash
• Dyspepsia
• Liver enzyme abnormalities
• Pruritus
• Taste disturbance
• Nausea
• Abdominal pain
• Flatulence

Practical Prescribing Details

• Can be taken with or without food (absorption not affected) 3
• Continuous daily dosing is superior to pulse dosing regimens 8
• A study comparing continuous vs. intermittent dosing found pulse therapy significantly less effective (5.8-5.9% lower cure rates) with no safety advantages 8

When Terbinafine May Not Be First-Line

• Candida onychomycosis: Azoles (itraconazole or fluconazole) are preferred 1
• Microsporum tinea capitis: Griseofulvin is superior 3
• Patients with multiple drug interactions involving CYP2D6 substrates may benefit from alternative therapy 2, 3