Lactolose: Common spelling variant of Lactulose (osmotic laxative)

Lactolose is a common spelling variant of the active substance Lactulose (with u in the middle) used in the population. Both terms refer to exactly the same active substance, a synthetic disaccharide composed of galactose and fructose, which is used as an osmotic laxative and for hepatic encephalopathy. A comprehensive pillar page with the correct spelling can be found at /wirkstoff/lactulose.

Lactulose was synthesized in the 1950s and has since been one of the most frequently prescribed gastrointestinal medications in Germany. Well-known brand names include Bifiteral, Lactulose AL, Lactulose Stada, and Duphalac. The active substance is available both over-the-counter in pharmacies and as a prescription medication and is offered in various dosage forms (syrup, powder, solution).

Mechanism of Action

Lactulose is not broken down or absorbed in the human small intestine because our digestive enzymes cannot break the specific bond between galactose and fructose. The substance reaches the colon unchanged, where bacteria (primarily bifidobacteria and lactobacilli) ferment it into short-chain fatty acids such as lactic acid, acetic acid, and butyric acid.

Three effects explain the clinical action:

First, the resulting acids osmotically bind water in the intestinal lumen, the stool becomes softer and more voluminous, and peristalsis increases (laxative effect).

Second, the acids lower the pH in the colon. Ammonia (NH3) from protein metabolism is protonated to ammonium (NH4+) and can barely cross the intestinal wall, so less nitrogen returns to the blood. This effect is therapeutically utilized in hepatic encephalopathy.

Third, the acidic, carbohydrate-rich environment promotes the growth of saccharolytic bacteria over proteolytic ones, further reducing ammonia production.

Indications

• Chronic and acute constipation: suitable for adults, children, pregnant women, and nursing mothers
• Hepatic encephalopathy: treatment and secondary prophylaxis in liver cirrhosis, standard according to DGVS and EASL guidelines
• Stool softener after perianal procedures, for hemorrhoids, anal fissure
• Irritable bowel syndrome with constipation: as an option alongside Macrogol
• Geriatric patients: opioid-induced constipation, immobility-related constipation

Dosage and Administration

Constipation in adults: initially 15 to 45 ml syrup per day, followed by a maintenance dose of 15 to 30 ml. Children up to 6 years: 5 ml/day, gradually adjusted. Infants: starting with 1 to 3 ml/day.

Hepatic encephalopathy: acutely 30 to 45 ml three times daily orally, with a target of two to three soft stools per day. In comatose patients, administration as a rectal lactulose enema 300 ml in 700 ml water, every 4 to 6 hours, until patient is responsive.

Onset of action: the laxative effect occurs after 1 to 2 days because the bacteria in the colon need time for fermentation. Too rapid dose escalation typically leads to bloating without significant additional effect.

Side Effects

Common: bloating, abdominal cramps, nausea, especially in the first few days or with rapid dose escalation. With proper dose titration, these symptoms usually resolve within a week.

Occasional to rare: diarrhea with electrolyte disturbances (hypokalemia, hypernatremia) from overdose, dehydration in elderly people with reduced fluid intake, allergic reactions.

Important: Lactulose is contraindicated in galactose intolerance, hereditary fructose intolerance, glucose-galactose malabsorption, or mechanical ileus. In case of suspected subileus, consult your doctor.

Drug Interactions

• Antibiotics (Neomycin, Rifaximin): can reduce lactulose fermentation and thus dampen the ammonia-lowering effect; in hepatic encephalopathy, the combination is nevertheless often deliberately used
• Gastric acid blockers (PPI, H2 blockers): no direct pharmacokinetic conflict
• Other laxatives: additive effect, risk of diarrhea
• Potassium-depleting diuretics: risk of hypokalemia increases

Special Precautions

Pregnancy and breastfeeding: Lactulose is considered the first-line agent for pregnant women with constipation, as it is not absorbed and does not enter breast milk.

Onset of action: Patients should know that lactulose, unlike stimulants (bisacodyl, senna), acts with a delay. For acute fecal retention, stimulating laxatives are more appropriate.

Hepatic encephalopathy as a therapeutic goal: The aim is not the strongest possible diarrhea, but two to three soft stools per day. Overdosing with profuse diarrhea increases the risk of dehydration and electrolyte shifts, which in turn can worsen encephalopathy.

Taste: some patients find the syrup unpleasantly sweet. When diluted in water or juice, it is better tolerated.

You May Also Be Interested In

• Lactulose, comprehensive pillar page
• Laktulose, German spelling variant
• Macrogol, alternative osmotic laxative (PEG)
• Bisacodyl, stimulating laxative
• Rifaximin, non-absorbable antibiotic for hepatic encephalopathy

Frequently Asked Questions

Sources

• Gelbe Liste, Lactulose active substance profile
• AWMF S2k Guideline chronic constipation and DGVS Guideline liver cirrhosis
• BfArM, Federal Institute for Drugs and Medical Devices
• EASL Clinical Practice Guidelines, hepatic encephalopathy