Lactulose
A synthetic sugar laxative for constipation that also lowers blood ammonia in hepatic encephalopathy.
Drug card
- Class
- Osmotic laxative
- How it works
- Holding water in the bowel by osmosis to soften and loosen stool
- Used for
- Constipation
- Hepatic encephalopathy: prevention and treatment
- Known for
- Flatulence and belching
- Bloating
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does lactulose work?
A disaccharide of galactose and fructose that human gut enzymes do not split, so it reaches the colon intact. Colonic bacteria ferment it to short acids (lactic, acetic and formic acid) that pull water into the bowel and acidify it. The acid turns ammonia into ammonium, which cannot be absorbed and leaves in the stool, so blood ammonia falls.
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 lactulose used for?
- Constipation
- Hepatic encephalopathy: prevention and treatment
Side effects
Side effects of lactulose
- Flatulence and belchingKnown for
- BloatingKnown for
- Abdominal cramps
- Nausea and vomiting
- Diarrhea with excess doses
- Fluid loss and dehydrationSerious
- Low potassiumSerious
- High sodium (hypernatremia)Serious
- Allergic reactions, including anaphylaxisSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- It contains some galactose: contraindicated for patients who need a low-galactose diet.
- Hydrogen can build up in the colon: cleanse the bowel with a non-fermentable solution before electrocautery.
- In diabetes, the high doses used for hepatic encephalopathy can affect blood glucose.
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:
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
Lactulose 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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