ALLYLAMINES
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.
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