Mechanism of action of terbinafine is?

Antifungal Drugs: CLASS IFICATION 1. Antibiotics A. Polyenes:AmphotericinB (AMB),Nystatin, Hamycin, Natamycin (Pimaricin) B. Heterocyclic benzofuran: Griseofulvin 2. Antimetabolite Flucytosine (5-FC) 3 Azofes A. lmidazoles (topical): Clotrimazole, Econazole, Miconazole, Oxiconazole (systemic): Ketoconazole B. Triazoles (systemic): Fluconazole, Itraconazole, Voriconazole 4. Allylamine: Terbinafine 5. Other topical agents Tolnaftate, Undecylenic acid, Benzoic acid, Quiniodochlor, Ciclopirox olamine, Butenafine, Sod. thiosulfate. TERBINAFI N E This orally and topically active drug against dermatophytes and Candida belongs to a new allylamine class of antifungals. In contrast to azoles which are primarily fungistatic, terbinafine is fungicidal: shoer courses of therapy are required and relapse rates are low. It acts as a non-competitive inhibitor of &;squalene epoxidase&;, an early step enzyme in ergosterol biosynthesis by fungi. Accumulation of squalene within fungal cells appears to be responsible for the fungicidal action. The mammalian enzyme is inhibited only by 1000-fold higher concentration of terbinafine. Approximately 75% of oral terbinafine is absorbed, but only 5% or less from unbroken skin. First pass metabolism fuher reduces oral bioavailability. lt is lipophilic, widely distributed in the body, strongly plasma protein bound and concentrated in sebum, stratum corneum and nail plates. It is inactivated by metabolism and excreted in urine (80%) and faeces (20%); elimination :plasma half life of l l-16 hr is prolonged to 10 days after repeated dosing. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:757,765