Macrogol
An osmotic laxative (polyethylene glycol 3350) for constipation and fecal impaction, and with salts for bowel cleansing before colonoscopy.
Also called polyethylene glycol 3350 (US name) or PEG 3350 (abbreviation).
Drug card
- Class
- Osmotic laxative
- How it works
- Holding water in the bowel by osmosis to soften and loosen stool
- Used for
- Constipation, including fecal impaction
- Bowel cleansing before colonoscopy
- Known for
- Bloating and abdominal fullness
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does macrogol work?
A polyethylene glycol polymer that keeps water in the bowel by osmosis, raising the water content of stool and speeding its passage. For bowel cleansing it comes as an iso-osmotic solution with salts, drunk in large volumes to wash out the colon.
Like other osmotic laxatives: Osmotic laxatives stay in the bowel and hold water there by osmosis. The extra water softens the stool, increases its volume and speeds its passage. Lactulose is also fermented by colonic bacteria into acids that add to this pull. They usually take 1 to 3 days to work, so they relieve constipation steadily rather than within hours.
Uses
What is macrogol used for?
- Constipation, including fecal impaction
- Bowel cleansing before colonoscopy
Side effects
Side effects of macrogol
- Bloating and abdominal fullnessKnown for
- Nausea and vomiting
- Abdominal cramps and pain
- Flatulence
- Diarrhea
- Low sodium and other salt imbalance (bowel prep)Serious
- Arrhythmias (bowel prep)Serious
- Seizures from salt imbalance (bowel prep)Serious
- Kidney injury (bowel prep)Serious
- Swelling of the hands or feet (edema)
- High potassiumSerious
- Allergic reactions, including anaphylaxisSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Contraindicated with bowel obstruction or perforation, ileus, gastric retention, and toxic colitis or megacolon.
- For bowel cleansing, keep patients hydrated and check salts, kidney function or the ECG in those at risk.
- It can flush other oral medicines out of the gut: give them about an hour apart from it.
- Avoid stimulant laxatives during bowel cleansing: together they raise the risk of ischemic colitis.
Remember it
A way to remember it
Osmotic laxatives are water magnets.
They stay in the bowel and hold water there by osmosis, which softens the stool; enough fluid helps them work and guards against dehydration.
Written for biofideX
Its class
Osmotic laxatives
Other osmotic laxatives with a card:
Easily mixed up with stimulant laxatives.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Polyethylene glycol 3350 powder: label (DailyMed)
- PEG 3350 and electrolytes for oral solution: label (DailyMed)
- Macrogol 3350-Based Iso-Osmotic Laxative (NCI Thesaurus)
- Macrogol (NHS)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Stomach and gut
Macrogol is one of 15 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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