Terbinafine HCL is an antifungal, which is highly hydrophobic and tends to accumulate in hair, skin, nails, and fatty tissue.

Terbinafine hydrochloride is a white fine crystalline powder that is freely soluble in methanol and dichloromethane, 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 cell membrane synthesis pathway. Because terbinafine prevents conversion of squalene to lanosterol, ergosterol cannot be synthesize.

1. Terbinafine is mainly effective on the dermatophyte group of fungi.
2. As a 1% cream or powder, it is used topically for superficial skin infections such as jock itch (tinea cruris), athlete's foot (tinea pedis), and other types of ringworm (tinea corporis). Terbinafine cream works in about half the time required by other antifungals.
3. Oral 250mg tablets are often prescribed for the treatment of onychomycosis, a fungal nail infection, typically by a dermatophyte or Candida species. Fungal nail infections are located 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 monitored with liver function tests. Alternatives to oral administration have been studied. 
4. Terbinafine may induce or exacerbate subacute cutaneous lupus erythematosus. Persons with lupus erythematosus should first discuss possible risks with their doctor before initiation of therapy.