Lactulose is a synthetic disaccharide used for the treatment of constipation and hepatic encephalopathy. It is not absorbed by the small intestine and, by an osmotic effect, deposits a large amount of fluid into the large intestine. The volume of fluid and the acid pH stimulate peristalsis. The low pH also discourages the growth of ammonia-producing organisms and reduces the absorption of ammonium ions and other nitrogenous compounds, which is why it is of benefit in patients with hepatic encephalopathy.

Indications.
Adult
PO
- Constipation. Initial: 10-20 g (15-30 mL)/day as a single dose or in 2 divided doses, up to 45 mL (solution) or 40 g (reconstituted powder)/day, adjust according to response.
- Hepatic encephalopathy 60-100 g (90-150 mL)/day in 3 divided doses, adjust as necessary to produce 2-3 soft stools/day.
Rectal
- Hepatic encephalopathy. Mix 200 g (300 mL) w/ 700 mL of water or NaCl 0.9%, as a retention enema over 30-60 min, repeat 4-6 hourly until oral medication is possible.

Adverse drug reactions
Abdominal discomfort (e.g., flatulence, cramps), nausea, and vomiting.

Adapted from CIMS Drug Information System. Internet. Accessed on March 3, 2017.