The allylamines (naftifine hydrochloride and terbinafine hydrochloride) are reversible noncompetitive inhibitors of the fungal enzyme squalene monooxygenase (squa-lene 2,3-epoxidase), which coverts squalene to lanos-terol. With a decrease in lanosterol production, ergos-terol production is also diminished, affecting fungal cell membrane synthesis and function. These agents gener-ally exhibit fungicidal activity against dermatophytes and fungistatic activity against yeasts.
Naftifine hydrochloride (Naftin) is available for top-ical use only in the treatment of cutaneous dermato-phyte and Candida infections; it is as effective as topical azoles for these conditions.
Terbinafine hydrochloride (Lamisil) is available for topical and systemic use (oral tablet) in the treatment of dermatophyte skin and nail infections. Terbinafine also exhibits in vitro activity against filamentous and dimor-phic fungi, but its clinical utility in treating infections with these organisms has not yet been established. It is used most commonly in the treatment of onychomyco-sis; in this setting, terbinafine is superior to griseofulvin and at least equivalent to itraconazole. When given sys-temically, terbinafine is 99% protein bound and accu-mulates in fat, skin, and nails, persisting for weeks. Cerebrospinal fluid penetration is less than 10%. Dosage reductions are required with renal or hepatic insufficiency. Although terbinafine has little effect on hepatic cytochrome P450 enzyme systems, it does mini-mally enhance cyclosporine clearance. Oral terbinafine is generally well tolerated but occasionally causes gas-tric distress and liver enzyme elevation.