Terbinafine achieves fungicidal activity in onychomycosis by inhibiting which enzyme, and what is the resulting biochemical consequence?

• A Squalene epoxidase, causing squalene accumulation and membrane disruption ✓
• B Lanosterol 14-alpha-demethylase, blocking ergosterol synthesis
• C Beta-1,3-glucan synthase, preventing cell wall assembly
• D Fungal topoisomerase II, arresting nuclear division

Explanation

Terbinafine selectively inhibits fungal squalene epoxidase, an early step in ergosterol biosynthesis upstream of lanosterol demethylase. Squalene accumulates to toxic concentrations and ergosterol falls, giving fungicidal action against dermatophytes. Azoles act at lanosterol 14-alpha-demethylase, which makes option B the strongest distractor. Terbinafine accumulates in keratin and nails, permitting short courses for nail infection, but can cause taste disturbance and hepatotoxicity.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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