It is a synthetic allylamine antifungal. It is highly lipophilic in nature and tends to accumulate in skin, nails, and fatty tissues. Like other allylamines, terbinafine inhibits ergosterol synthesis by inhibiting the fungal squalene monooxygenase (squalene 2,3-epoxidase), an enzyme that is part of the fungal cell wall synthesis pathway. Indication For the treatment of dermatophyte infections of the toenail or fingernail caused by susceptible fungi. Also for the treatment of tinea capitis (scalp ringworm) and tinea corporis (body ringworm) or tinea cruris (jock itch). Associated Conditions Candidiasis, Cutaneous Onychomycosis Pityriasis versicolor Sporotrichosis Tinea Capitis Tinea Corporis Tinea Cruris Tinea Pedis Pharmacodynamics Terbinafine is an allylamine antifungal agent and acts by inhibiting squalene epoxidase, thus blocking the biosynthesis of ergosterol, an essential component of fungal cell membranes. In vitro, mammalian squalene monooxygenase (squalene 2,3-epoxidase) is only inhibited at higher (4000 fold) concentrations than is needed for inhibition of the dermatophyte enzyme. Depending on the concentration of the drug and the fungal species test in vitro, Terbinafine may be fungicidal. However, the clinical significance of in vitro data is unknown. Mechanism of action Terbinafine is hypothesized to act by inhibiting squalene monooxygenase, thus blocking the biosynthesis of ergosterol, an essential component of fungal cell membranes. This inhibition also results in an accumulation of squalene, which is a substrate catalyzed to 2,3-oxydo squalene by squalene monooxygenase. The resultant high concentration of squalene and decreased amount of ergosterol are both thought to contribute to terbinafine's antifungal activity.