nystatin
Summary
Nystatin is a polyene antifungal used primarily for Candida infections, particularly oral thrush, esophageal candidiasis, and cutaneous/vaginal candidiasis. It is not absorbed systemically when given orally, so it is used topically or as a 'swish and swallow' for mucosal infections rather than for systemic treatment.
Detail
Mechanism: Nystatin binds ergosterol in the fungal cell membrane, forming pores that increase membrane permeability, leading to leakage of intracellular contents and fungal cell death. This mechanism is similar to amphotericin B, as both are polyene antifungals that target ergosterol, a sterol unique to fungal (not human) cell membranes, providing selective toxicity.
Clinical use: Nystatin is too toxic for IV use and poorly absorbed from the GI tract, making it ideal for topical or mucosal application. Common formulations include oral suspension ('swish and swallow' or 'swish and spit') for oropharyngeal candidiasis (thrush), especially in immunocompromised patients (HIV/AIDS, chemotherapy patients, denture wearers, inhaled corticosteroid users), vaginal tablets/creams for candidal vaginitis, and topical creams/powders for cutaneous candidal infections (e.g., diaper rash, intertriginous candidiasis).
Spectrum: Active against Candida species but not effective against dermatophytes or systemic fungal infections (no activity against Aspergillus, Cryptococcus, etc.).
Adverse effects: Minimal systemic toxicity due to lack of absorption. Oral formulations may cause GI upset (nausea, diarrhea) or a bad taste. Topical use is generally very well tolerated.
Board relevance: Commonly tested in contrast to amphotericin B (systemic use, nephrotoxicity, IV administration) and azoles (fluconazole, itraconazole - systemic absorption, CYP450 interactions). Key teaching point: nystatin = topical/mucosal Candida treatment only, due to toxicity profile preventing systemic use and poor oral bioavailability.
Sources
- First Aid for the USMLE Step 1
- Katzung's Basic and Clinical Pharmacology
- Goodman & Gilman's The Pharmacological Basis of Therapeutics
Reviewed by Medusa editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.