Systemic Antifungal — Onychomycosis / Tinea Pregnancy: Available postmarketing data in pregnant women are insufficient to evaluate a drug-associated risk of major birth defects, miscarriage or adverse maternal or fetal outcomes. In animal reproduction studies terbinafine caused no malformations or fetal harm in pregnant rabbits and rats dosed during organogenesis at up to 12 and 23 times the maximum recommended human dose of 250 mg/day respectively.

Terbinafine (Oral)

Brand names: Lamisil

An oral allylamine antifungal used as a first-line systemic treatment for dermatophyte infections, especially fungal nail disease (onychomycosis) and tinea capitis.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 250 mg (one tablet)

Route: Oral

Frequency: Once daily

SOURCING NOTE: the eMC record pulled into this bundle is the SPC for 'Terbinafine 1 % Cream' — a topical product, the wrong formulation for this oral page — so its posology was deliberately NOT used. The dose above is from the US prescribing information for terbinafine 250 mg tablets (Preferred Pharmaceuticals Inc., label date 2025-09-30); clinician to confirm against the UK SPC for terbinafine 250 mg tablets, which also carries the tinea corporis/cruris/pedis and hepatic/renal dosing content absent from the US label. US label §2.2: fingernail onychomycosis — one 250 mg tablet once daily for 6 weeks; toenail onychomycosis — one 250 mg tablet once daily for 12 weeks. The optimal clinical effect is seen some months after mycological cure and cessation of treatment, reflecting the period required for outgrowth of healthy nail. Before administering, evaluate patients for evidence of chronic or active liver disease; obtain pretreatment serum transaminases and assess liver function before and periodically during therapy, discontinuing if liver injury develops. Discontinue if taste or smell disturbance occurs (may be severe, prolonged or permanent) and if the neutrophil count falls to 1000 cells/mm³ or below. In the elderly, dose selection should be cautious, usually starting at the low end of the dosing range. PAEDIATRIC: safety and efficacy of terbinafine tablets have not been established in paediatric patients with onychomycosis — no paediatric dose is stated in this source; verify any paediatric use against a children's formulary.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Chronic or active liver disease
History of allergic reaction to oral terbinafine, because of the risk of anaphylaxis

Side effects

Headache
Diarrhoea, dyspepsia, abdominal pain, nausea and flatulence
Rash and pruritus (also urticaria)
Liver enzyme abnormalities — liver failure, sometimes leading to transplant or death, has occurred
Taste disturbance including taste loss, and smell disturbance including loss of smell — may be severe, prolonged or permanent
Serious skin reactions: Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema multiforme, exfoliative dermatitis, bullous dermatitis and DRESS; also severe neutropenia and depressive symptoms

Interactions

Terbinafine is an inhibitor of CYP2D6 — coadminister drugs predominantly metabolised by CYP2D6 (tricyclic antidepressants, SSRIs, beta-blockers, class 1C antiarrhythmics such as flecainide and propafenone, and MAO type B inhibitors) with careful monitoring; a dose reduction of the CYP2D6 substrate may be required
Desipramine — terbinafine produced a 2-fold rise in Cmax and a 5-fold rise in AUC, persisting to the last observation 4 weeks after terbinafine was stopped
Drug interactions have also been noted with cimetidine, fluconazole, ciclosporin, rifampicin and caffeine

Clinical monograph

How it works

Terbinafine inhibits the fungal enzyme squalene epoxidase, blocking ergosterol biosynthesis; this depletes the fungal cell membrane of ergosterol and causes toxic accumulation of squalene, producing a fungicidal effect against dermatophytes.

Prescribing in practice

Rare but serious idiosyncratic hepatotoxicity can occur, so it should be avoided in active or chronic liver disease and stopped immediately if symptoms or signs of liver injury (jaundice, dark urine, unexplained nausea) develop.
It can cause taste disturbance and, rarely, severe cutaneous reactions and blood dyscrasias, and may exacerbate or precipitate cutaneous and systemic lupus erythematosus.
It inhibits CYP2D6, so check for interactions with substrates such as tricyclic antidepressants and certain beta-blockers and antiarrhythmics.

Monitoring

Check liver function before starting prolonged oral courses and monitor during treatment, advising the patient to report any signs of liver toxicity or skin reaction.

Counselling the patient

Take the course exactly as prescribed; nail infections require several months of treatment for the nail to grow out clear.
Report jaundice, dark urine, pale stools, persistent nausea, marked fatigue or any rash promptly.
A temporary disturbance or loss of taste can occur and usually recovers after stopping.

Evidence & guidelines

Oral terbinafine is established as the most effective treatment for dermatophyte onychomycosis, with higher mycological cure rates than oral azoles in trial evidence.

Reference: BAD Onychomycosis Guidelines 2014; NICE CKS Fungal Nail Infection; Cochrane (Bell-Syer et al. 2012); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Itraconazole · Systemic Antifungal — Onychomycosis / Tinea

Pathways