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 12 weeks for toenails and 6 weeks for fingernails, as this represents the most effective oral antifungal with superior cure rates and minimal drug interactions. 1, 2, 3

Standard Adult Dosing

Onychomycosis (Nail Infections):

• Toenail infections: 250 mg once daily for 12 weeks 4, 1, 2, 3
• Fingernail infections: 250 mg once daily for 6 weeks 4, 2, 3
• Can be taken with or without food 2
• Re-evaluate patients 3-6 months after treatment initiation, as clinical improvement continues after therapy completion due to terbinafine's persistence in nail tissue 1, 5

Pediatric Dosing

For onychomycosis in children, use weight-based dosing: 4, 2

• <20 kg: 62.5 mg daily
• 20-40 kg: 125 mg daily
• >40 kg: 250 mg daily (adult dose)
• Duration: 6 weeks for fingernails, 12 weeks for toenails

For tinea capitis (scalp ringworm): 5

• Same weight-based dosing as above
• Duration: 2-4 weeks
• Critical caveat: Terbinafine is highly effective against Trichophyton species but significantly less effective against Microsporum species—use griseofulvin for Microsporum infections 2

Special Populations

Diabetic patients: Terbinafine is the preferred oral antifungal due to low risk of drug interactions and hypoglycemia, plus lower cardiac risk compared to itraconazole 4

Immunosuppressed patients (HIV, transplant recipients): Terbinafine and fluconazole are preferred over itraconazole/ketoconazole due to reduced risk of interactions with antiretrovirals and immunosuppressants 4

Pre-Treatment Requirements

Mandatory baseline testing: 1, 2, 3

• Liver function tests (ALT and AST)
• Complete blood count, particularly in patients with history of hepatitis, heavy alcohol use, or hematological abnormalities 2
• Mycological confirmation (KOH preparation and/or fungal culture) before initiating treatment 1

More vigilant monitoring required for: 1

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

Absolute Contraindications

1, 2, 3

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

Critical Safety Warnings

Discontinue terbinafine immediately if any of these occur: 1, 3

Hepatotoxicity: Liver failure requiring transplant or resulting in death has occurred 3

• Monitor for: nausea, vomiting, right upper quadrant pain, jaundice, dark urine, pale stools, fatigue

Taste disturbance: Can be severe, prolonged, or permanent 1, 3

• Stop medication if taste changes occur

Smell disturbance: May be prolonged or permanent 1, 3

• Stop medication if smell changes occur

Severe skin reactions: Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS syndrome 1, 2, 3

• Stop immediately if progressive skin rash, blistering, or mucosal involvement develops

Severe neutropenia: Discontinue if neutrophil count ≤1,000 cells/mm³ 3

Depressive symptoms: Monitor for mood changes, loss of interest, sleep disturbances 1, 3

Drug Interactions

Terbinafine has minimal drug interactions compared to azole antifungals, making it safer for polypharmacy patients. 1, 2

Primary interaction concern: Inhibition of cytochrome P450 2D6 enzyme 1, 2, 3

• Affects metabolism of: certain antidepressants (desipramine), beta-blockers, antiarrhythmics 2, 3
• Also interacts with: cimetidine, fluconazole, cyclosporine, rifampin, caffeine 3

Comparative Efficacy

Terbinafine demonstrates superior efficacy to itraconazole for dermatophyte onychomycosis with higher cure rates and lower relapse rates. 1, 5, 2

• Fungicidal against dermatophytes with very low minimum inhibitory concentrations (approximately 0.004 μg/mL) 1, 5, 2
• Mycological cure rates of 72-77% at 72 weeks for toenail onychomycosis 6
• Clinical cure rates improve after treatment cessation due to drug persistence in nail tissue for up to 6 months 2
• More effective than griseofulvin for dermatophyte infections 7, 8

Common Pitfalls to Avoid

• Do not use terbinafine for Candida onychomycosis—azoles (itraconazole or fluconazole) are preferred 4
• Do not use for Microsporum tinea capitis—griseofulvin is superior 2
• Do not assume 6 weeks is sufficient for toenails—this consistently shows inferior cure rates compared to 12 weeks 9
• Do not skip baseline liver function tests—hepatotoxicity can be severe and unpredictable 1, 2, 3
• Do not continue therapy if taste or smell disturbances develop—these may become permanent 1, 3