What infections are treated with oral terbinafine 250 mg once daily and what are the typical treatment durations?

Terbinafine 250mg Daily: Indications and Treatment Durations

Terbinafine 250 mg once daily is primarily used to treat fungal nail infections (onychomycosis) and dermatophyte skin infections, with treatment durations ranging from 2-4 weeks for skin infections to 6-12 weeks for nail infections depending on the site affected. 1, 2, 3

Primary Indications

Onychomycosis (Fungal Nail Infections)

• Fingernail infections: 6 weeks of continuous therapy 1, 3
• Toenail infections: 12 weeks of continuous therapy (up to 16 weeks for severe cases) 1, 3
• The optimal clinical effect appears months after treatment completion due to the time required for healthy nail outgrowth 3
• Terbinafine persists in the nail for up to 30 weeks after treatment cessation, allowing continued fungicidal activity 1

Cutaneous Dermatophyte Infections (Ringworm)

• Tinea corporis/cruris (body/groin ringworm): 2-4 weeks when systemic therapy is indicated 2
• Tinea pedis (athlete's foot): 2-4 weeks for extensive infections or those involving hair follicles 2
• Oral therapy is warranted for extensive infections, follicular involvement, or failure of topical treatment within 2 weeks 2

Tinea Capitis (Scalp Ringworm)

• Highly effective against Trichophyton species: 2-4 weeks of treatment 1
• Significantly less effective against Microsporum species: griseofulvin is superior and should be used instead 1
• Topical therapy alone is inadequate; oral therapy is generally required 2

Critical Pre-Treatment Requirements

Before initiating terbinafine, obtain baseline laboratory tests 1, 2, 3:

• Liver function tests (ALT and AST) are mandatory 1, 3
• Complete blood count is required 1, 2
• These are particularly important in patients with history of hepatitis, heavy alcohol use, or hematological abnormalities 1, 2

Absolute Contraindications

Do not prescribe terbinafine in the following situations 1, 2, 3:

• Active or chronic liver disease 1, 2
• Lupus erythematosus 1, 2
• Known allergy to oral terbinafine 3
• Pregnancy (should not be started during pregnancy) 3

Why Terbinafine is First-Line for Dermatophyte Infections

Terbinafine demonstrates superior efficacy compared to alternatives 1, 4:

• Fungicidal against dermatophytes with very low minimum inhibitory concentrations (approximately 0.004 μg/mL) 1
• Higher complete cure rates and lower relapse rates compared to itraconazole 1, 4
• The L.I.ON. study showed mycological cure rates of 76-81% with terbinafine versus 38-49% with itraconazole at 72 weeks 4
• At 5-year follow-up, terbinafine maintained superior complete cure rates (35% vs 14%) with lower relapse rates (23% vs 53%) compared to itraconazole 4

Pediatric Dosing

Weight-based dosing for children 1, 2:

• Children <20 kg: 62.5 mg daily 1, 2
• Children 20-40 kg: 125 mg daily 1, 2
• Children >40 kg: 250 mg daily (adult dose) 1, 2
• Duration: 6 weeks for fingernails, 12 weeks for toenails 1
• For tinea capitis: 2-4 weeks depending on organism 1

Safety Profile and Common Adverse Effects

Terbinafine is generally well tolerated with an incidence of serious adverse events of only 0.04% 1, 2:

• Gastrointestinal disturbances (49% of reported side effects): nausea, diarrhea, abdominal pain 1, 2
• Dermatological reactions (23%): rash, pruritus, urticaria 2
• Headache 1
• Taste disturbance 1, 3

Serious but rare adverse events requiring immediate discontinuation 1, 3:

• Stevens-Johnson syndrome and toxic epidermal necrolysis 1
• Hepatotoxicity (persistent nausea, jaundice, dark urine, pale stools) 3
• Subacute lupus-like syndrome 1

Drug Interaction Advantages

Terbinafine has minimal drug-drug interactions compared to azole antifungals 1, 2:

• The only potentially significant interaction involves drugs metabolized by cytochrome P450 2D6 (certain antidepressants, beta-blockers, antiarrhythmics) 1, 2
• This makes terbinafine safer for patients on multiple medications 1

Practical Prescribing Details

• Can be taken with or without food, as absorption is not affected by food intake 1
• If a dose is missed, take as soon as remembered unless less than 4 hours before the next dose 3
• Re-evaluate patients 3-6 months after treatment initiation; if disease persists, additional treatment can be started immediately without waiting 1

Important Clinical Caveat

For Candida onychomycosis, itraconazole is preferred over terbinafine due to broader antimicrobial coverage 1. Confirm the causative organism before selecting therapy, as terbinafine's superior efficacy is specific to dermatophyte infections 1, 4.