Lactulose
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Lactulose
Kristalose, Constulose, Generlac, Enulose
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Summary
Common uses
Chronic constipation0, Hepatic encephalopathy (acute and chronic)0
Pharmacy
Starting dose
Constipation: 15-30 mL PO daily (titrate to 1-2 soft stools/day); hepatic encephalopathy: 20-30 g (30-45 mL) PO/PR every 1-2 hours acutely until soft stools, then BID-QID to target 2-3 soft stools/day
Preparations
10 g/15 mL solution (Constulose); 10 g, 20 g powder packets (Kristalose)
US FDA Max
Indication-specific; HE may require high-volume dosing
Pharmacology
Routes
Oral, rectal (enema, especially in acute HE)
Onset
Constipation: 24-48 hours; HE: ammonia reduction within hours of stool production
Duration
Hours
Half-life
Not meaningfully described — lactulose is not significantly absorbed
Bioavailability
<3% systemic absorption (the basis of the safety and mechanism)[1]
Pregnancy
Generally considered safe (minimal systemic absorption).[citation needed]
Legal status
Rx-only in US
Purported mechanism
Lactulose is a non-absorbable synthetic disaccharide (galactose-fructose) that passes intact to the colon where bacterial fermentation produces short-chain fatty acids, lowering luminal pH and trapping ammonia as non-absorbable ammonium ion (NH₄⁺); the same fermentation also produces an osmotic load that draws water into the lumen, softening stool.0 In hepatic encephalopathy, both mechanisms (ammonia trapping AND laxation that purges nitrogenous waste from the gut) contribute to ammonia reduction. Cathartic flatulence is the universal side effect; dehydration with overuse can paradoxically precipitate HE[1].
References
- ↑ 1.0 1.1 FDA Prescribing Information, Kristalose (lactulose), Mission Pharmacal, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/020706s015lbl.pdf