What are the indications for terbinafine?

What is Terbinafine For?

Terbinafine is an allylamine antifungal medication used primarily to treat fungal infections of the nails (onychomycosis), skin (tinea infections including athlete's foot, jock itch, and ringworm), and scalp (tinea capitis in children ≥4 years). 1

FDA-Approved Indications

• Onychomycosis (nail fungus): Terbinafine is FDA-approved for treating toenail and fingernail infections caused by dermatophytes (tinea unguium). 1
• The standard adult dosing is 250 mg once daily for 6 weeks for fingernail infections and 12 weeks for toenail infections (up to 16 weeks for severe cases). 2, 1

Additional Clinical Uses

Tinea Pedis (Athlete's Foot)

• Oral terbinafine 250 mg once daily for 1 week provides comparable efficacy to 4 weeks of twice-daily topical clotrimazole, with faster clinical resolution. 3
• Topical terbinafine 1% formulations applied once or twice daily for up to 2 weeks achieve mycological cure in >80% of patients. 4

Tinea Capitis (Scalp Ringworm) in Children

• Terbinafine oral granules are FDA-approved for children ≥4 years of age specifically for tinea capitis. 2
• Critical caveat: Terbinafine is highly effective against Trichophyton species (2-4 weeks treatment) but significantly less effective against Microsporum species—griseofulvin is superior for Microsporum infections. 2
• Obtain scalp scrapings/hair pluck for culture to identify the causative organism before initiating therapy. 2

Other Dermatophyte Infections

• Tinea corporis/cruris (body/groin ringworm): Oral terbinafine achieves mycological cure in approximately 90% of patients. 5
• Cutaneous candidiasis and pityriasis versicolor: Topical terbinafine has been effective in approximately 80% of patients, though it has fungistatic (not fungicidal) activity against Candida albicans. 5, 4

Why Terbinafine is First-Line for Dermatophyte Infections

• Superior efficacy: Terbinafine demonstrates higher complete cure rates and lower relapse rates compared to itraconazole, fluconazole, and griseofulvin for dermatophyte onychomycosis. 2, 6
• Fungicidal mechanism: Terbinafine inhibits squalene epoxidase, causing ergosterol depletion (fungistatic effect) and toxic squalene accumulation (fungicidal effect) in fungal cells. 6
• Prolonged tissue persistence: Terbinafine persists in nails for 6 months after treatment completion due to its lipophilic and keratophilic properties, allowing continued antifungal activity. 2, 7
• Minimal drug interactions: Unlike azole antifungals, terbinafine has minimal drug-drug interactions, making it safer for patients on multiple medications. 2, 6

Key Contraindications and Safety Warnings

Absolute Contraindications

• Active or chronic liver disease is an absolute contraindication. 2, 8
• Lupus erythematosus is an absolute contraindication. 2
• Renal impairment (creatinine clearance ≤50 mL/min) is a contraindication, as terbinafine is primarily cleared by the kidneys. 8
• History of allergic reaction to oral terbinafine due to risk of anaphylaxis. 1

Critical Safety Warnings

• Hepatotoxicity: Liver failure, sometimes leading to liver transplant or death, has occurred with oral terbinafine use. 1
• Taste and smell disturbances: Can be severe, prolonged, or permanent—discontinue terbinafine if these occur. 8, 1
• Severe skin reactions: Stevens-Johnson syndrome, toxic epidermal necrolysis, and DRESS syndrome have been reported. 2, 1
• Hematologic effects: Severe neutropenia has been reported; discontinue if neutrophil count ≤1,000 cells/mm³. 1

Pre-Treatment Requirements

• Baseline liver function tests (ALT, AST) and complete blood count are required before initiating therapy. 2, 8
• Particularly important in patients with history of hepatitis, heavy alcohol use, or hematological abnormalities. 2
• For high-risk patients (prior liver disease, concurrent hepatotoxic drugs), obtain weekly LFTs for the first two weeks, then every two weeks for the first two months. 8

Monitoring During Treatment

• For low-risk patients with normal baseline liver tests, routine periodic monitoring is not required unless treatment extends beyond one month or clinical symptoms develop. 8
• Discontinue terbinafine immediately if biochemical evidence of liver injury or clinical symptoms of hepatotoxicity develop (jaundice, dark urine, persistent nausea/vomiting, unexplained fatigue, severe rash). 8
• If AST/ALT ≥5× upper limit of normal or rising bilirubin occurs during treatment, discontinue immediately. 8

Pediatric Dosing

• Children <20 kg: 62.5 mg daily 2
• Children 20-40 kg: 125 mg daily 2
• Children >40 kg: 250 mg daily (adult dose) 2
• Duration: 6 weeks for fingernail and 12 weeks for toenail infections 2

Common Adverse Effects

• Gastrointestinal disturbances (49% of reported side effects): nausea, diarrhea, abdominal pain 2, 1
• Dermatological events (23%): rash, pruritus, urticaria 8
• Headache 2, 1
• Taste disturbance 2, 1
• Liver enzyme abnormalities 1