Terbinafine is an allylamine medicine used to treat fungal infections. It is especially effective against dermatophytes (tinea infections). Terbinafine inhibits a fungal enzyme, squalene epoxidase, and stops the cells making ergosterol, the main component of the cell wall.
Terbinafine inhibits an enzyme essential for the production of substances vital for the reproduction and survival of some types of fungal organisms. Terbinafine is an allylamine structurally related to naftifine. It is a synthetic antifungal agent. It is highly lipophilic in nature and tends to accumulate in skin, nails, and fatty tissues. As with the other allylamines, terbinafine inhibits ergosterol biosynthesis via inhibition of squalene epoxidase. This enzyme is part of the fungal sterol synthesis pathway that creates the sterols needed for the fungal cell membrane. Terbinafine is an allylamine antifungal active against many fungal pathogens particularly dermatophtes. Like most other systemic antifungals terbinafine acts at the fungal cell membrane where it reduces ergosterol synthesis. Dermatophytes and other filamentous fungi are more susceptible to terbinafine than yeast although the mycelial phase of candida is susceptible. Terbinafine is active against Trypanosoma cruzi and Leishmania mexicana. It is absorbed well when taken orally, with or without food. It is bound to proteins such as albumin in the circulating blood and becomes concentrated in fat cells and within skin and nails. It is slowly eliminated in faeces and urine mostly after conversion by the liver into inactive compounds. Doses may need to be reduced in the presence of kidney disease.
Action/Kinetics: Inhibits squalene epoxidase, a key enzyme in the sterol biosynthesis in fungi. Results in ergosterol deficiency and a corresponding accumulation of squalene leading to fungal cell death. Approximately 75% of cutaneously absorbed drug is excreted in the urine, mostly as metabolites. Well absorbed following PO administration, with first-pass metabolism being about 40%. Peak plasma levels: 1 mcg/mL within 2 hr. Food enhances absorption. Over 99% bound to plasma proteins. Slowly excreted from adipose tissue and skin. Extensively metabolized with about 70% of the dose eliminated in the urine. Renal or hepatic disease decreases clearance from the body.
Uses: Topical use: Interdigital tinea pedis (athletes' foot), tinea cruris (jock itch), or tinea corporis (ringworm) due to Epidermophyton floccosum, Trichophyton mentagrophytes or T. rubrum. Plantar tinea pedis. Tinea versicolor due to Malassezia furfur. Investigational: Cutaneous candidiasis and tinea versicolor.Oral use: Onychomycosis of the toenail or fingernail due to dermatophytes.