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Systemic Antifungal — Onychomycosis / Tinea Pregnancy: Avoid unless essential — limited data; BAD recommends waiting until after pregnancy for onychomycosis treatment

Terbinafine (Oral)

Brand names: Lamisil

Adult dose

Dose: 250 mg once daily
Route: Oral
Frequency: Once daily
Max: 250 mg/day
First-line systemic treatment for dermatophyte onychomycosis (toenails: 12 weeks; fingernails: 6 weeks) and tinea capitis. Fungicidal against dermatophytes (Trichophyton, Epidermophyton, Microsporum) — inhibits ergosterol synthesis via squalene epoxidase inhibition. Less effective against Candida onychomycosis — itraconazole preferred for Candida.

Paediatric dose

Dose: Weight-based: <20 kg 62.5 mg OD; 20–40 kg 125 mg OD; >40 kg 250 mg OD mg/kg
Route: Oral
Frequency: Once daily
Max: 250 mg/day
BNFc: licensed for tinea capitis in children. Tablet can be crushed and mixed with food. Duration: tinea capitis 4 weeks; onychomycosis 12 weeks (toenails).

Dose adjustments

Renal

Avoid if eGFR <50 mL/min/1.73m² (limited data; terbinafine accumulates)

Hepatic

Avoid in active or chronic liver disease — hepatotoxicity risk

Paediatric weight-based calculator

BNFc: licensed for tinea capitis in children. Tablet can be crushed and mixed with food. Duration: tinea capitis 4 weeks; onychomycosis 12 weeks (toenails).

Clinical pearls

  • First-line for dermatophyte onychomycosis — mycological cure rate ~70–80% at 12 weeks; superior to itraconazole for Trichophyton rubrum (most common UK species)
  • Nail culture/microscopy mandatory before prescribing — confirms dermatophyte infection; avoid empirical treatment of nail dystrophy
  • Taste disturbance (ageusia): reversible in most patients but can persist for weeks-months after stopping — counsel patients before initiating
  • Hepatotoxicity: rare but can be severe; check LFTs at baseline for prolonged courses; stop immediately if symptomatic liver disease
  • CYP2D6 inhibition: clinically significant interactions with metoprolol, propranolol (bradycardia risk), TCAs, SSRIs — review medications before prescribing
  • Tinea capitis: terbinafine for Trichophyton species (most common); griseofulvin preferred for Microsporum canis (better efficacy in this species)

Contraindications

  • Active liver disease
  • Hypersensitivity to terbinafine

Side effects

  • GI disturbance (nausea, diarrhoea, abdominal pain)
  • Taste disturbance/loss (ageusia — uncommon; may persist after stopping)
  • Hepatotoxicity (rare but serious — check LFTs if symptomatic)
  • Skin reactions (rash, urticaria)
  • Stevens-Johnson syndrome/TEN (rare)
  • Lupus-like syndrome (rare)

Interactions

  • Warfarin — may alter INR (both increased and decreased reported; monitor)
  • CYP2D6 substrates — terbinafine inhibits CYP2D6; increased levels of TCAs, SSRIs, beta-blockers (metoprolol, propranolol)
  • Rifampicin — reduces terbinafine levels by 100%
  • Cimetidine — increases terbinafine levels

Monitoring

  • LFTs (baseline; if symptomatic during treatment)
  • Mycological cure at 3–6 months post-treatment
  • Taste disturbance

Reference: BNFc; BNF 90; BNFc; BAD Onychomycosis Guidelines 2014; NICE CKS Fungal Nail Infection; Cochrane (Bell-Syer et al. 2012). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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