[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Laxatives](https://durgical.com/en/pharmacology/classes/laxatives/) › Macrogol (polyethylene glycol)

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# Macrogol (polyethylene glycol)

An inert, non-absorbed polymer that holds water in the bowel and softens stool. Also used, with salts, to clean the colon before colonoscopy.

Updated 2026-11-01

- Class: [Laxatives](https://durgical.com/en/pharmacology/classes/laxatives/)
- Target: Colonic lumen (osmotic water retention)
- ATC code: A06AD15

Also called: Polyethylene glycol, PEG 3350, PEG 4000

## Mechanism of action

Macrogol is a large, inert polymer that is not absorbed or broken down by colonic bacteria. Its molecules hold water in the bowel by osmosis, so stools become larger, softer and more frequent. Because bacteria do not ferment it, it causes less gas and cramping than lactulose or sorbitol. Bowel-preparation solutions add sodium, potassium, chloride, bicarbonate and sulfate so large volumes cause little net shift of fluid or electrolytes.

- Inert polymer: not absorbed, not fermented
- Holds water in the bowel lumen by osmosis
- Larger, softer stools trigger more frequent bowel movements

## Pharmacokinetics

**Absorption**
Essentially not absorbed

**Metabolism**
Not broken down by colonic bacteria

**Elimination**
In the stool

**Onset and duration**
For constipation, a bowel movement usually comes in 1 to 3 days

## Indications

- Constipation in adults and children [Constipation and faecal impaction →](https://durgical.com/en/conditions/constipation-and-faecal-impaction/)
- Faecal impaction [Constipation and faecal impaction →](https://durgical.com/en/conditions/constipation-and-faecal-impaction/)
- Bowel preparation before colonoscopy (with electrolytes)

## Adverse effects

### Common

- Bloating
- Abdominal pain and cramps
- Flatulence
- Nausea or vomiting
- Diarrhoea

### Serious (rare, important)

- Allergic reactions including anaphylaxis
- High potassium or oedema with electrolyte-containing products

## Contraindications

- Allergy to polyethylene glycol
- Known or suspected bowel obstruction
- Kidney disease without medical supervision

## Key interactions

**Starch-based thickeners for swallowing problems**
The label warns against combining them; patients who need thickened liquids are given a different plan

**Other oral medicines**
Faster transit can reduce their absorption; they are usually given at least an hour apart

## What is monitored

- Stool frequency and consistency
- Diarrhoea, which signals an excessive dose
- Fluid and electrolyte balance in heart or kidney disease and during bowel preparation

## Administration and safety

- The powder is fully dissolved in a drink before it is taken; it is not swallowed with clumps.
- Not mixed with starch-based thickeners used in dysphagia.
- During bowel preparation the patient keeps drinking clear fluids to stay hydrated.

## Nursing care

- Check for signs of bowel obstruction (vomiting, distension, severe pain) before starting.
- Record stool output and report diarrhoea.
- In bowel preparation, watch for dizziness, weakness and dehydration, especially in older adults.
- Teach to space other medicines from the dose and to report rectal bleeding.

## Pregnancy and breastfeeding

Considered suitable in pregnancy and breastfeeding because it is barely absorbed.

## Memory aid

Macrogol is a «water magnet» the bacteria ignore: no fermentation, little gas.

## Test yourself

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

## Why does macrogol cause less gas than lactulose?

Colonic bacteria do not ferment it, so little gas is produced.

## Why are electrolytes added to macrogol bowel-preparation solutions?

So that large volumes clean the colon without causing important net shifts of fluid or electrolytes.

## Which swallowing aid should not be mixed with macrogol?

Starch-based thickeners used in dysphagia; the product label warns against combining them.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/macrogol/)

## Related drugs

- [Lactulose](https://durgical.com/en/pharmacology/lactulose/)
- [Bisacodyl](https://durgical.com/en/pharmacology/bisacodyl/)
- [Senna](https://durgical.com/en/pharmacology/senna/)

## Related conditions

- [Constipation and faecal impaction](https://durgical.com/en/conditions/constipation-and-faecal-impaction/)

[← Back to the class: Laxatives](https://durgical.com/en/pharmacology/classes/laxatives/)

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 - POLYETHYLENE GLYCOL 3350 powder, for solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=2f5c975f-0d35-4f68-a27c-28af9a898733) (DailyMed (U.S. National Library of Medicine), 2026); [Polyethylene Glycol 3350: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a603032.html) (MedlinePlus (U.S. National Library of Medicine), 2016); [Macrogol: a laxative medicine to treat constipation - NHS](https://www.nhs.uk/medicines/macrogol/) (NHS (National Health Service, UK), 2026); Farmacología básica y clínica (Katzung), 16.ª ed., cap. 62 (McGraw Hill, 2025).

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Representative model, for educational purposes only.

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