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Generic name: lactulose systemic

Brand names: Constulose, Kristalose, Enulose, Generlac, Chronulac, Cephulac, Constilac, Cholac, Duphalac, Evalose, Heptalac, Chronulac Syrup

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product

Packet, Oral:

Kristalose: 10 g (30 ea); 20 g (30 ea)

Generic: 10 g (15 ea)

Solution, Oral:

Constulose: 10 g/15 mL (237 mL, 946 mL) [unflavored flavor]

Enulose: 10 g/15 mL (473 mL) [unflavored flavor]

Generlac: 10 g/15 mL (473 mL, 1892 mL) [unflavored flavor]

Generic: 10 g/15 mL (15 mL, 30 mL, 236 mL [DSC], 237 mL, 473 mL, 480 mL [DSC], 500 mL [DSC], 946 mL, 1892 mL [DSC]); 20 g/30 mL (30 mL)


Mechanism of Action

The bacterial degradation of lactulose resulting in an acidic pH inhibits the diffusion of NH3 into the blood by causing the conversion of NH3 to NH4+; also enhances the diffusion of NH3 from the blood into the gut where conversion to NH4+ occurs; produces an osmotic effect in the colon with resultant distention promoting peristalsis; reduces blood ammonia concentration to reduce the degree of portal systemic encephalopathy





Via colonic flora to lactic acid and acetic acid; requires colonic flora for drug activation


Primarily feces; urine (≤3%)

Onset of Action

Constipation: Up to 24 to 48 hours to produce a normal bowel movement

Encephalopathy: At least 24 to 48 hours

Use: Labeled Indications

Constipation (Constulose, Kristalose): Treatment of constipation

Portal systemic encephalopathy (Enulose, Generlac): Prevention and treatment of portal-systemic encephalopathy (including hepatic precoma and coma)

Use: Off Label

Minimal hepatic encephalopathyayes

A meta-analysis and randomized controlled trials confirm the effectiveness of lactulose in the treatment of hepatic encephalopathy. The American Association for the Study of Liver Diseases guidelines for the management of hepatic encephalopathy in patients with chronic liver disease state that lactulose is generally used as initial treatment for overt hepatic encephalopathy and is recommended for prevention of recurrent episodes of hepatic encephalopathy after the initial episode.


Patients requiring a low galactose diet

Dosage and Administration

Dosing: Adult

Constipation: Oral: 10 to 20 g (15 to 30 mL or 1 to 2 packets) daily; may increase to 40 g (60 mL or 2 to 4 packets) daily if necessary

Portal systemic encephalopathy (PSE), prevention: Oral: 20 to 30 g (30 to 45 mL) 3 to 4 times daily; adjust dose every 1 to 2 days to produce 2 to 3 soft stools/day

PSE treatment:

Oral: 20 to 30 g (30 to 45 mL) every 1 hour to induce rapid laxation; reduce to 20 to 30 g (30 to 45 mL) 3 to 4 times daily after laxation is achieved to produce 2 to 3 soft stools/day

Rectal administration (retention enema): 200 g (300 mL) via rectal balloon catheter; retain for 30 to 60 minutes; may repeat every 4 to 6 hours; transition to oral treatment prior to discontinuing rectal administration

Overt hepatic encephalopathy (OHE) episodes, treatment: Route not specified: 16.7 g (25 mL) every 1 to 2 hours until at least 2 soft or loose bowel movements are produced daily; titrate to maintain 2 to 3 bowel movements daily (AASLD [Vilstrup 2014]).

Minimal hepatic encephalopathy (off-label use): 20 to 40 g (30 to 60 mL) daily in 2 to 3 divided doses to maintain 2 to 3 bowel movements daily for up to 3 months (Dhiman 2000; Watanabe 1997; Prasad 2007)

Dosing: Geriatric

Refer to adult dosing.

Dosing: Pediatric

Note: Doses in pediatric patients may be expressed in volume (mL) or weight (g); use extra precaution.

Constipation; chronic: Limited data available: Infants, Children, and Adolescents: Oral: 1 to 2 g/kg/day (1.5 to 3 mL/kg/day) divided once or twice daily (NASPGHAN [Tabbers 2014]); maximum daily dose: 60 mL/day in adults

Constipation, palliative care: Limited data available: Children and Adolescents: Oral: 2 to 30 mL every 6 to 24 hours (Johnston 2005), others have suggested 5 to 10 mL every 2 hours until bowel movement (Kliegman 2011)

Fecal impaction, slow disimpaction: Limited data available: Infants, Children, and Adolescents: Oral: 1.33 g/kg/dose (2 mL/kg) twice daily for 7 days (Wyllie 2011; Pashankar 2005)

Portal systemic encephalopathy, prevention: Oral liquid:

Infants: 1.7 to 6.7 g/day (2.5 to 10 mL/day) in divided doses; adjust dosage to produce 2 to 3 stools/day

Children and Adolescents: 26.7 to 60 g/day (40 to 90 mL/day) in divided doses; adjust dosage to produce 2 to 3 stools/day


Oral solution: May mix with fruit juice, water or milk.

Crystals for oral solution: Dissolve contents of packet in 120 mL water.

Rectal: Dilute with 700 mL of water or NS; administer as retention enema using a rectal balloon catheter; retain for 30 to 60 minutes. May repeat enema immediately if inadvertently evacuated too promptly. Cleansing enemas containing soapsuds or other alkaline agents should not be used.

Dietary Considerations

Contraindicated in patients on galactose-restricted diet.


Store at room temperature; do not freeze. Protect from light. Discard solution if cloudy or very dark. Prolonged exposure to cold temperatures will cause thickening which will return to normal upon warming to room temperature.

Drug Interactions

Dichlorphenamide: Laxatives may enhance the hypokalemic effect of Dichlorphenamide. Monitor therapy

Glutamine: May diminish the therapeutic effect of Lactulose. Specifically, glutamine may diminish the ammonia-lowering effects of lactulose. Monitor therapy

Adverse Reactions

Frequency not defined.

Endocrine & metabolic: Dehydration, hypernatremia, hypokalemia

Gastrointestinal: Abdominal cramps, abdominal distention, abdominal distress, diarrhea (excessive dose), eructation, flatulence, nausea, vomiting


Concerns related to adverse effects:

  • Electrolyte imbalance: Monitor periodically for electrolyte imbalance when lactulose is used >6 months or in patients predisposed to electrolyte abnormalities (eg, elderly, debilitated patients). Hepatic disease may predispose patients to electrolyte imbalance. Infants receiving lactulose may develop hyponatremia and dehydration.

Disease-related concerns:

  • Diabetes: Use with caution in patients with diabetes mellitus; solution contains galactose and lactose.

Other warnings/precautions:

  • Electrocautery procedures: During proctoscopy or colonoscopy procedures involving electrocautery, a theoretical risk of reaction between H2 gas accumulation and electrical spark may exist; thorough bowel cleansing with a nonfermentable solution is recommended.

Monitoring Parameters

Blood pressure, standing/supine; serum electrolytes, serum ammonia; bowel movement patterns, fluid status


Pregnancy Risk Factor


Pregnancy Considerations

Adverse events have not been observed in animal reproduction studies. Lactulose is poorly absorbed following oral administration. Use of dietary fiber or bulk-forming laxatives along with increased fluid intake is generally considered first line therapy for treating constipation in pregnant women. Short-term use of lactulose is also considered to be safe/low risk when therapy is needed; however, side effects may limit its use (Cullen, 2007; Mahadevan, 2006; Prather, 2004; Wald, 2003).

Patient Education

What is this drug used for?

  • It is used to treat constipation.
  • It is used to treat or prevent certain brain or mental problems caused by liver disease. It may be used by mouth or rectally.
  • It may be given to you for other reasons. Talk with the doctor.

Frequently reported side effects of this drug

  • Burping
  • Abdominal cramps
  • Passing gas
  • Vomiting
  • Nausea

Other side effects of this drug: Talk with your doctor right away if you have any of these signs of:

  • High blood sugar like confusion, fatigue, increased thirst, increased hunger, passing a lot of urine, flushing, fast breathing, or breath that smells like fruit.
  • Diarrhea
  • Signs of a significant reaction like wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat.

Note: This is not a comprehensive list of all side effects. Talk to your doctor if you have questions.

Consumer Information Use and Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this medicine. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not specific medical advice and does not replace information you receive from the healthcare provider. You must talk with the healthcare provider for complete information about the risks and benefits of using this medicine.

Source: Wolters Kluwer Health. Last updated January 31, 2020.