Terbinafine

Terbinafine is an allylamine medicine used to treat fungal infections. It is especially effective against dermatophytes (tinea infections).

In New Zealand it is available as 250 mg tablets (Lamisil® & Terbafin®) and as a cream formulation (Lamisil®). The tablets require a doctor's prescription. Lamisil cream is available at a pharmacy without prescription.

Terbinafine inhibits a fungal enzyme, squalene epoxidase, and stops the cells making ergosterol, the main component of the cell wall.

It is absorbed well when taken orally, with or without food. It is bound to proteins such as albumin in the circulating blood and becomes concentrated in fat cells and within skin and nails. It is slowly eliminated in faeces and urine mostly after conversion by the liver into inactive compounds. Doses may need to be reduced in the presence of kidney disease.

Skin concentrations may be up to 75-fold higher than those in the blood. It may persist in the skin for up to 8 weeks after the drug has been discontinued and in the nails for up to a year.

Dose regime

Terbinafine cream is applied to the affected area twice daily for one to four weeks.

The oral dose for adults is 250 mg daily.

For children, the tablets can be hidden in food - the tablets taste unpleasant:

• Weight 10-20 kg, 62.5 mg per day
• Weight 20-40 kg, 125 mg per day
• Weight >40 kg, 250 mg per day

• Tinea corporis, tinea cruris, tinea pedis, tinea manuum: 1 to 4 weeks
• Tinea unguium: for 6-8 weeks (fingernails) or 3-4 months (toenails)

Treatment can be repeated if necessary.

Side effects

Terbinafine appears to be a relatively safe drug. Side effects, usually minor, arise occasionally. These include:

• Nausea, feeling of fullness.
• Diarrhoea, abdominal pain.
• Taste disturbance, loss of appetite (2%).
• Headache.
• Dizziness.
• Abnormal liver function tests (5%).
• Reduced neutrophil white blood cell count.
• Allergic skin rash including urticaria and erythema multiforme major (toxic epidermal necrolysis).

Terbinafine should not be taken in pregnancy or during breast-feeding.

Drug interactions

Terbinafine does not generally alter the concentration of other medications.

Rifampicin results in a slight decrease in the concentration of terbinafine. Cimetidine may slightly increase the concentration of terbinafine. Terbinafine is not thought to interact with the oral contraceptive pill.