Terbinafine

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Chapter: Essential pharmacology : Antifungal Drugs

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: shorter courses of therapy are required and relapse rates are low.


TERBINAFINE

 

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: shorter courses of therapy are required and relapse rates are low. It acts as a noncompetitive 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 1000fold higher concentration of terbinafine.

 

Approximately 75% of oral terbinafine is absorbed, but only 5% or less from unbroken skin. First pass metabolism further reduces oral bioavailability. It 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 t½ of 11–16 hr is prolonged to 10 days after repeated dosing.

 

Side effects of oral terbinafine are gastric upset, rashes, taste disturbance. Some cases of hepatic dysfunction, haematological disorder and severe cutaneous reaction are reported. Enzyme inducers lower, and enzyme inhibitors raise its steady-state plasma levels. Terbinafine does not inhibit CYP450.

 

Topical terbinafine can cause erythema, itching, dryness, irritation, urticaria and rashes.

 

Use

 

Terbinafine applied topically as 1% cream or orally 250 mg OD is indicated in tinea pedis/ corporis/cruris/capitis and pityriasis versicolor; 2–6 weeks treatment is required according to the site. Onychomycosis is treated by 3–12 months oral therapy. Efficacy in toe nail infection is 60–80%, which is higher than griseofulvin and itraconazole.

 

It is less effective against cutaneous and mucosal candidiasis: 2–4 weeks oral therapy may be used as an alternative to fluconazole.

 

LAMISIL, SEBIFIN, DASKIL 250 mg tab, 1% topical cream. EXIFINE 125, 250 mg tabs, 1% cream; TERBIDERM 1% cream.

 

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