Lactulose is a synthetic, non-absorbable disaccharide sugar (galactose and fructose) used primarily as an osmotic laxative for the treatment of chronic constipation and in the management of hepatic encephalopathy (portal-systemic encephalopathy). In the colon, it is metabolized by colonic bacteria to low molecular weight acids, acidifying the colonic contents, drawing water into the lumen, and promoting peristalsis. For hepatic encephalopathy, it reduces ammonia absorption by trapping it as ammonium ions in the acidic colon.
Adult: Constipation: Initially 15-30 ml (10-20g of lactulose) daily, adjusted to produce 1-2 soft stools per day. Maintenance: 10-25 ml daily. Hepatic Encephalopathy: Initial: 30-50 ml (20-33g) every 1-2 hours to induce rapid laxation, then adjusted to produce 2-3 soft stools daily. Typical maintenance: 30-45 ml (20-30g) 3-4 times daily.
Note: Can be taken with water, fruit juice, or milk to improve palatability. For precise dosing in hepatic encephalopathy, use a measuring cup or syringe. May be given via nasogastric tube. For laxative effect, take once daily, preferably in the morning. For hepatic encephalopathy, doses are divided. Do not take with antacids (may reduce efficacy).
Lactulose is a synthetic disaccharide that passes unchanged to the colon. Here, it is broken down by saccharolytic bacteria (primarily Lactobacillus and Bifidobacterium) into low molecular weight organic acids, primarily lactic acid and acetic acid, and small amounts of formic acid. This process acidifies the colonic contents (lowers pH to approximately 5). The increased osmotic load from these non-absorbable molecules and the acidic environment draws water into the colonic lumen, softening stool, increasing stool volume, and stimulating peristalsis, producing a laxative effect. In hepatic encephalopathy, the acidification of colonic contents converts ammonia (NH3) to the non-absorbable ammonium ion (NH4+), which is trapped and excreted in the feces. The acidic environment also favors the growth of non-urease-producing bacteria, further reducing ammonia production.
Pregnancy: Category B (US FDA). Animal studies show no risk, but no adequate, well-controlled studies in pregnant women. Use only if clearly needed. Considered safe for occasional use in pregnancy-related constipation.
Driving: No effect. However, drowsiness from hepatic encephalopathy itself may impair ability.
| Non-absorbable Antacids (e.g., Aluminum Hydroxide, Magnesium Hydroxide) | May neutralize the colonic acids produced by lactulose, reducing its effectiveness in treating hepatic encephalopathy. | Moderate |
| Other Laxatives | Additive effect, increasing risk of excessive diarrhea and electrolyte loss. | Moderate |
| Oral Medications (especially enteric-coated or delayed-release) | Diarrhea induced by lactulose may reduce gastrointestinal transit time, potentially decreasing absorption of co-administered drugs. | Moderate |
| Antibiotics (Neomycin, Metronidazole, Rifaximin) | May reduce colonic bacterial flora required to metabolize lactulose, potentially diminishing its effect. Often used synergistically in hepatic encephalopathy. | Moderate |