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Chapter: Basic & Clinical Pharmacology - Antifungal Agents

Oral Systemic Antifungal Drugs for Mucocutaneous Infections

Griseofulvin is a very insoluble fungistatic drug derived from a species of penicillium.

ORAL SYSTEMIC ANTIFUNGAL DRUGS FOR MUCOCUTANEOUS INFECTIONS

GRISEOFULVIN

Griseofulvin is a very insoluble fungistatic drug derived from a species of penicillium. Its only use is in the systemic treatment of dermatophytosis . It is administered in a micro-crystalline form at a dosage of 1 g/d. Absorption is improved when it is given with fatty foods. Griseofulvin’s mechanism of action at the cellular level is unclear, but it is deposited in newly forming skin where it binds to keratin, protecting the skin from new infec-tion. Because its action is to prevent infection of these new skin structures, griseofulvin must be administered for 2–6 weeks for skin and hair infections to allow the replacement of infected kera-tin by the resistant structures. Nail infections may require therapy for months to allow regrowth of the new protected nail and is often followed by relapse. Adverse effects include an allergic syn-drome much like serum sickness, hepatitis, and drug interactions with warfarin and phenobarbital. Griseofulvin has been largely replaced by newer antifungal medications such as itraconazole and terbinafine.

TERBINAFINE

Terbinafine is a synthetic allylamine that is available in an oral formulation and is used at a dosage of 250 mg/d. It is used in the treatment of dermatophytoses, especially onychomycosis . Like griseofulvin, terbinafine is a keratophilic medi-cation, but unlike griseofulvin, it is fungicidal. Like the azole drugs, it interferes with ergosterol biosynthesis, but rather than interacting with the P450 system, terbinafine inhibits the fungal enzyme squalene epoxidase (Figure 48–1). This leads to the accu-mulation of the sterol squalene, which is toxic to the organism. One tablet given daily for 12 weeks achieves a cure rate of up to 90% for onychomycosis and is more effective than griseofulvin or itraconazole. Adverse effects are rare, consisting primarily of gastrointestinal upset and headache. Terbinafine does not seem to affect the P450 system and has demonstrated no significant drug interactions to date.




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