Overview
Lactulose is a synthetic disaccharide laxative composed of galactose and fructose. It is primarily used for the treatment of chronic constipation and for the prevention and treatment of portal-systemic (hepatic) encephalopathy. It works locally in the colon and is minimally absorbed systemically.
Mechanism of Action
Lactulose is not absorbed in the small intestine and reaches the colon unchanged, where it is metabolized by colonic bacteria into low-molecular-weight organic acids (mainly lactic acid and acetic acid). This results in: Increased osmotic pressure → water retention in the colon → stool softening Acidification of colonic contents → conversion of ammonia (NH₃) to ammonium (NH₄⁺) Reduced systemic absorption of ammonia → decreased blood ammonia levels This mechanism is particularly important in hepatic encephalopathy.
Indications
- Chronic constipation
- Portal-systemic (hepatic) encephalopathy (for prevention and treatment of hyperammonemia)
Dosage
Constipation (Adults): Initial: 15–30 mL orally daily May be increased to 60 mL daily if needed Maintenance: Adjust to produce 2–3 soft stools per day Hepatic Encephalopathy (Adults): Initial: 30–45 mL orally 3–4 times daily Adjust dose to achieve 2–3 soft stools daily Rectal Administration (Hepatic Encephalopathy if needed): 300 mL lactulose in 700 mL water or saline as retention enema
Contraindications
- Hypersensitivity to lactulose
- Patients requiring a low-galactose diet
- Intestinal obstruction
Side Effects
- Flatulence
- Abdominal cramping
- Diarrhea
- Nausea
- Serious: Severe dehydration
- Serious: Hypokalemia
- Serious: Hypernatremia (with excessive diarrhea)
Interactions
- Other laxatives: Increased risk of excessive diarrhea and electrolyte imbalance
- Neomycin (for hepatic encephalopathy): May reduce lactulose effectiveness by altering gut flora
- Antacids: May reduce the acidification effect in the colon
Counseling Points
- Very sweet taste. Safe for children/elderly. OTC.