Lactulose
- Class: Osmotic laxative
- Used for: constipation
- Say it: LAK-tyoo-lohs
- Forms: oral liquid
LACTULOSE is a sugar you cannot absorb, so you LOSE it — and in liver failure the ammonia leaves with it.
Colonic bacteria ferment it into acids that trap ammonia as ammonium, which cannot be reabsorbed. Titrate to two or three soft stools a day, not to a volume.
Undigested in the small bowel, it is fermented by colonic bacteria into acids. Those acids hold water in the stool and trap ammonia as ammonium, which cannot be reabsorbed — so it leaves in the faeces.
Side effects
Common: bloating, gas, stomach cramps
Serious: dehydration, salt loss
Typical dose
15–30 mL daily; 30–45 mL three or four times daily in encephalopathy
Millilitres, not milligrams. Encephalopathy needs two to three times the daily amount used for simple constipation.
Check yourself
How does lactulose help hepatic encephalopathy?
- Colonic acidification traps ammonia as ammonium so it cannot be reabsorbed
- It binds ammonia in the bloodstream directly
- It stops the liver producing ammonia
- It blocks ammonia receptors in the brain
Show answer
A. Colonic acidification traps ammonia as ammonium so it cannot be reabsorbed
Bacterial fermentation lowers colonic pH, converting absorbable ammonia into non-absorbable ammonium. Combined with faster transit, that removes nitrogen from the body — which is why the dose is titrated to stool frequency.
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