lactulose

Action and Spectrum

Lactulose is a synthetic disaccharide composed of galactose and fructose. It reaches the colon unchanged, where it is broken down by saccharolytic bacteria into organic acids such as lactic acid, formic acid, and acetic acid. These acids, along with gases like hydrogen and methane, enhance peristalsis, increase stool water content via osmotic action, and soften stool, thereby promoting bowel movements. However, this laxative effect may take 24–48 hours to manifest. 

In addition to its laxative effect, lactulose acidifies the colon contents, which is beneficial in treating portal-systemic encephalopathy (PSE). The acidic environment facilitates the conversion of ammonia (NH₃) into non-absorbable ammonium ions (NH₄⁺), thus reducing systemic ammonia levels. Furthermore, the acidic environment inhibits urease-producing bacteria and supports ammonia utilization by gut bacteria for protein synthesis, enhancing ammonia excretion. 

Drug Interaction

Adverse Reaction

Adverse drug reactions:   

Frequency Not Defined 

Abdominal distention 

Belching 

Flatulence 

Dehydration 

Hypokalemia 

Nausea 

Vomiting 

Diarrhea 

Excessive bowel activity 

Hypernatremia 

Abdominal cramping 

Black Box Warning

Do not use if you are allergic to lactulose or any of its components. Keep out of reach of children. In case of overdose, seek immediate medical attention or contact a Poison Control Center. 

Contraindication / Caution

Contraindication 

Galactosemia 

Cautions 

Use caution in patients with diabetes, as the formulation contains lactose and galactose. Long-term use (over 6 months) or use in individuals prone to electrolyte disturbances requires monitoring for imbalances. Concurrent use of other laxatives should be avoided. The effectiveness of lactulose may be reduced when taken alongside anti-infective agents. 

Pregnancy / Lactation

Pregnancy warnings:     

Pregnancy category: B 

Breastfeeding warnings:  

• The release of the drug into the human breastmilk is unknown  

Pregnancy Categories:       

Category A: Satisfactory and well-controlled studies show no risk to the fetus in the first trimester or the later trimester.       

Category B: No evidence shown of risk to the fetus found in animal reproduction studies, and there are not enough studies on pregnant women       

Category C: Adverse effects on the fetus found with evidence in animal reproduction studies and no adequate evidence for a result in humans must take care of potential risks in pregnant women       

Category D: There is adequate data available with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits       

Category X: Drugs listed in this category outweigh risks over benefits. Hence these categories of drugs need to be avoided by pregnant women.       

Category N: There is no data available for the drug under this category

Pharmacology

Lactulose is a synthetic, non-absorbable disaccharide composed of galactose and fructose. It exerts its primary pharmacological effects within the gastrointestinal tract due to minimal systemic absorption. In the colon, it is metabolized by saccharolytic bacteria into short-chain organic acids such as lactic acid, acetic acid, and formic acid. 

These acids lower colonic pH and exert an osmotic effect, drawing water into the bowel, increasing stool volume, and softening stool—resulting in enhanced peristalsis and bowel movement frequency. This makes lactulose effective as a laxative for treating constipation. 

Additionally, the acidification of colonic contents plays a therapeutic role in hepatic encephalopathy by converting diffusible ammonia (NH₃) into non-absorbable ammonium ions (NH₄⁺), which are then excreted in the stool. This reduces systemic ammonia levels. The acidic environment also suppresses ammonia-producing bacteria and promotes the use of ammonia by colonic bacteria for protein synthesis. 

Pharmacokinetics 

Absorption 

Less than 3% is absorbed from the small intestine; most reaches the colon unabsorbed. 

Distribution 

Remains localized in the gastrointestinal tract; systemic distribution is negligible. 

Metabolism 

Metabolized in the colon by saccharolytic bacteria into lactic, acetic, and formic acids. 

Elimination/Excretion 

Less than 3% is renally excreted within 24 hours; the rest is excreted in feces. 

Pharmacodynamics 

Lactulose is primarily administered orally or rectally and is minimally absorbed in the gastrointestinal tract. As a result, its pharmacologic actions are largely confined to the gut. It works by increasing stool volume and softening stool, which enhances bowel movements. These effects can lead to gastrointestinal symptoms such as increased bowel sounds (borborygmi), bloating, belching, flatulence, and diarrhea. 

Adminstartion

Lactulose is administered either orally or rectally. Oral doses can be taken with or without food and may be diluted with water, juice, or milk to improve palatability. Accurate measurement with a dosing device is recommended. In patients unable to take oral medication, lactulose can be given rectally as an enema, particularly in cases of hepatic encephalopathy. Rectal administration should be retained for 30–60 minutes if possible. The laxative effect typically begins within 24 to 48 hours. 

Patient Information Leaflet

Generic Name: lactulose 

Pronounced: LAK-chuh-lohs 

Why do we use lactulose?  

Lactulose is a prescription medication used orally or rectally to treat or prevent complications of liver disease, particularly hepatic encephalopathy. It helps improve mental status by lowering blood ammonia levels. Additionally, it is used as a laxative to relieve constipation. It acts as a colonic acidifier.