Terbinafine (Oral)

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.