Terbinafine

What terbinafine tablets are for

Terbinafine works through the whole body rather than sitting on the surface of the skin. It is used for fungal infections of the nails — onychomycosis, where the fungus has worked its way into the nail itself — and for skin infections such as ringworm, jock itch and athlete's foot when the patch is too widespread, too thick or too stubborn for a cream to clear. Because the tablet reaches the nail bed and the deeper layers of skin, it can deal with infections that a topical treatment cannot. It has no effect on bacterial rashes or eczema.

How terbinafine works

Fungi need a substance called ergosterol to build a sturdy cell membrane. Terbinafine blocks squalene epoxidase, the enzyme that produces it. Without ergosterol the membrane fails, and squalene, a by-product of the same pathway, builds up to toxic levels inside the fungal cell. The fungus stops growing and dies off. Terbinafine is drawn to fat and keratin, so it collects in skin and nail, which is why a course keeps working on the nail long after the final tablet.

Taking the tablets

One 250mg tablet a day does the job. Food is not a factor: breakfast, dinner or an empty stomach all work equally well. Fingernail infections are usually treated for six weeks and toenail infections for twelve, because the toenail grows more slowly. Do not judge the result by how the nail looks when the course ends — the fungus may already be gone while the damaged nail is still growing out, and a nail can take several months to look normal again. If a tablet is missed and the next one is due within four hours, leave the missed dose out and carry on as before; taking two at once is not the answer.

Side effects and interactions

Headache, diarrhoea, indigestion, nausea and a mild rash are the effects people notice most often. A changed sense of taste is peculiar to terbinafine — food can taste metallic, salty or simply flat, and it sometimes takes weeks to settle after the course ends. Rarely, terbinafine harms the liver or the blood cells, or triggers a serious skin reaction; yellowing of the eyes or skin, dark urine and persistent nausea are signs of liver trouble, while a spreading rash, fever or swelling of the face and throat needs urgent treatment. Terbinafine also blocks CYP2D6, a liver enzyme that clears some antidepressants, beta-blockers and heart-rhythm medicines, so those can build up in the body while you take it. Cimetidine, a heartburn medicine, raises terbinafine levels, and rifampicin lowers them.

Lamisil 250mg tablets

Lamisil is the brand name for terbinafine, and it comes here as 250mg tablets — the strength used in adult treatment. Creams and other tablets for fungal infections sit together under antifungals.