Terbinafine hydrochloride (Lamisil® in UK & US) is a synthetic allylamine antifungal. It is highly lipophilic in nature and tends to accumulate in skin, nails, and fatty tissues.

Pharmacology

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Terbinafine hydrochloride is a white fine crystalline powder that is freely soluble in methanol and methylene chloride, soluble in ethanol, and slightly soluble in water.

Like other allylamines, terbinafine inhibits ergosterol synthesis by inhibiting squalene epoxidase -- an enzyme that is part of the fungal sterol synthesis pathway that creates the sterols needed for the fungal cell membrane. In layman's terms, it inhibits fungal and bacterial cell wall growth, causing the contents of the cell to be unprotected and eventually die.

Indications

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Terbinafine is mainly effective on the dermatophytes group of fungi.

As a 1% cream or powder it is used for superficial skin infections such as jock itch (Tinea cruris), athlete's foot (Tinea pedis) and Ringworm.

Oral 250mg tablets are often prescribed for the treatment of onychomycosis of the toenail or fingernail due to the dermatophyte Tinea unguium. Fungal nail infections are located live deep under the nail in the cuticle to which topically applied treatments are unable to penetrate in sufficient amounts. The tablets may rarely cause hepatotoxicity, so patients are warned of this and may be monitered with liver function tests.

Specific US issues

Many health insurance companies consider these infections to be a cosmetic problem, and either do not cover the cost of the months-long course of Lamisil, which can run into the thousands of dollars, or recommend use of less expensive alternatives like fluconazole.

Antifungals | Novartis