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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Polyene antifungals

Antifungals that bind ergosterol and open holes in the fungal membrane. Amphotericin B goes by vein; nystatin works only on skin and mucosa.

Updated 2026-11-01

## What they are

Large ring-shaped molecules made by Streptomyces bacteria. Amphotericin B is the broad, fungicidal drug for life-threatening invasive mycoses; nystatin is barely absorbed and is used only locally for Candida in the mouth, gut and skin.

## Mechanism of action

Polyenes bind ergosterol, the main sterol of fungal membranes, and group into channels that let potassium and other ions leak out until the cell dies. They also bind cholesterol in human membranes, less strongly, which explains amphotericin B's kidney and infusion toxicity.

Target: Ergosterol in the fungal cell membrane

## Key points

- Bind ergosterol and form pores: fungicidal, broad spectrum.
- Amphotericin B: fever and rigors during the infusion, nephrotoxicity, low potassium and magnesium.
- Conventional and lipid amphotericin B are dosed differently and are not interchangeable: mixing them up has caused fatal overdoses.
- Amphotericin B plus flucytosine is the classic induction for cryptococcal meningitis.
- Nystatin is not absorbed: only for oral, intestinal and skin candidiasis, never for systemic mycoses.

## Drugs in this class

- [**Amphotericin B** Polyene antifungal given by vein for life-threatening fungal infections. It opens pores in the fungal membrane but can… Ergosterol in the fungal cell membrane (a sterol, not a protein)](https://durgical.com/en/pharmacology/amphotericin-b/)
- [**Nystatin** Polyene antifungal that is not absorbed from the gut or skin. Used as an oral liquid or cream for thrush and Candida… Ergosterol in the fungal cell membrane (a sterol, not a protein)](https://durgical.com/en/pharmacology/nystatin/)

## Others in the class

- natamycin (eye drops)

## Test yourself

Think of the answer, then tap the question to see it.

## Why does amphotericin B damage human cells at all?

It prefers ergosterol but also binds cholesterol in human membranes, especially in the kidney tubule, which causes leaks and nephrotoxicity.

## Can nystatin treat candidaemia?

No. It is almost not absorbed from the gut or skin, so it only acts where it is applied: mouth, gut or skin.

## Which two electrolytes are watched most closely with amphotericin B?

Potassium and magnesium, which are lost through the damaged kidney tubule.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - AMPHOTERICIN B injection, powder, lyophilized, for solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a0a54943-9ce4-4f3e-b681-a1a9144c16ce) (DailyMed (U.S. National Library of Medicine), 2022); [DailyMed - AMPHOTERICIN B injectable, liposomal](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=02aadef1-390b-4270-b56d-33452eb89dde) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - NYSTATIN ORAL SUSPENSION- nystatin suspension](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4a670371-d373-1ba6-e063-6394a90a13b6) (DailyMed (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 61 (McGraw Hill, 2023).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/classes/polyene-antifungals/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/polyene-antifungals/