Dentosphere : World of Dentistry: Broad-spectrum antifungal used only as a topical agent because of renal toxicity is:

# Broad-spectrum antifungal used only as a topical agent because of renal toxicity is:

A. Miconazole

B. Nystatin

C. Amphotericin B

D. Clotrimazole

The correct answer is B. Nystatin.

Nystatin is a polyene antifungal antibiotic (similar in structure and mechanism to Amphotericin B).

Mechanism: It binds to ergosterol in the fungal cell membrane, creating pores that cause leakage of intracellular contents (potassium and other ions), leading to fungal cell death.
Toxicity: While it has a broad spectrum of activity, it is never used parenterally (systemically) because of its severe systemic toxicity, particularly nephrotoxicity.
Usage: It is not significantly absorbed from the gastrointestinal tract, skin, or mucous membranes. Therefore, it is safe and effective when used topically (e.g., oral suspensions for oral candidiasis, creams for skin infections) to treat local infections without causing systemic side effects.

A. Miconazole: An imidazole antifungal. While largely used topically (e.g., Daktarin gel), it can be administered systemically (IV) for severe infections (though less common now due to newer drugs). Its primary systemic concern is usually related to hepatic enzymes (CYP450 inhibition), not the severe direct renal toxicity seen with polyenes.
C. Amphotericin B: Also a polyene antifungal with the same mechanism as Nystatin. It is notoriously nephrotoxic (often called "Ampho-terrible"). However, unlike Nystatin, it is used systemically (IV) for life-threatening systemic fungal infections because it is the "gold standard" for efficacy, despite the risk of kidney damage. The prompt asks for a drug used only topically.
D. Clotrimazole: An imidazole typically restricted to topical use (troches, creams) because of significant gastrointestinal intolerance and hepatic enzyme induction if given systemically. It is not primarily restricted due to renal toxicity.