Terbinafine (Lamisil): fungal skin and nail treatment

Terbinafine kills fungus by damaging its cell membrane, according to the NHS. The infections it treats include athlete's foot, fungal infections of the nails, ringworm, jock itch, pityriasis versicolor and candida infections of the skin.

Which form you need depends on where the infection is. Skin infections often clear with an over-the-counter cream, gel, spray or solution, whereas nail infections and resistant infections usually need tablets prescribed by a doctor.

Apply cream, gel or spray to the infected area once or twice a day for 1 to 2 weeks. Many fungal infections get better within that time, and the NHS suggests talking to a doctor if symptoms persist beyond 2 weeks.

The solution, Lamisil Once, is a single application, after which you should not wash your feet for 24 hours. Complete the course even if the skin looks better, because stopping early risks the infection returning. Over-the-counter cream, gel and spray are for ages 16 and over and the solution is for 18 and over.

Tablets are one a day, swallowed with water, with or without food. Treatment time varies from 2 to 4 weeks for jock itch to 3 months or more for nails. Fungal nail infections are slow because the nail has to grow out: the NHS notes nail infections can need 6 months or more, particularly on the big toe.

Long-term use carries a small risk to the liver, under 1 in 1,000, so doctors may arrange blood tests to check liver function. Wait at least 7 days after finishing tablets before donating blood.

• Missed dose: take or apply it when you remember unless the next is near; do not double up.

• Call NHS 111 if 4 or more tablets are taken at once, or if 2 or more extra tablets cause side effects.

Tell the prescriber or pharmacist about earlier allergic reactions to terbinafine or other medicines, liver problems, kidney problems, and whether you are pregnant, trying to conceive or breastfeeding.

Topical forms most often cause peeling or itching skin at the site, in more than 1 in 100 people. Tablets can cause rash, headache, diarrhoea, nausea or vomiting, reduced appetite, taste changes, stomach ache, indigestion, joint pain, dizziness and vision problems.

• Call NHS 111 for yellow skin or eyes with pale stools and dark urine, easy bruising or frequent infections, fever with a rash and unusual tiredness, severe upper abdominal pain spreading to the back, or muscle weakness with dark red-brown urine.

• Call 999 if the lips, mouth, throat or tongue suddenly swell, or you have difficulty breathing.

Terbinafine tablets can interact with antidepressants, beta blockers, oral contraceptives, amiodarone, ciclosporin, cimetidine, rifampicin, tamoxifen and warfarin. Paracetamol, ibuprofen, diclofenac and naproxen are compatible, but terbinafine tablets may reduce the effect of codeine or increase the side effects of tramadol. Limit caffeine, which terbinafine may amplify.

Topical forms carry little interaction risk.

Tablets are not generally recommended in pregnancy, while cream, gel and spray show no evidence of harm. Topical terbinafine is very unlikely to reach breast milk, but wash your hands after use and keep it away from the breasts and the baby's skin. Small amounts of tablets pass into milk, so discuss alternatives, and watch for poor feeding, vomiting, jaundice or rash.

Alcohol is fine. Drive only if you feel well. Suspected side effects can be reported through the Yellow Card scheme.