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Medically reviewed on Dec 4, 2018


(LAK tyoo lose)

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, 500 mL [DSC], 946 mL, 1892 mL [DSC]); 20 g/30 mL (30 mL)

Brand Names: U.S.

  • Constulose
  • Enulose
  • Generlac
  • Kristalose

Pharmacologic Category

  • Ammonium Detoxicant
  • Laxative, Osmotic


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)

Off Label Uses

Subclinical (minimal) hepatic encephalopathy

Evidence-based guidelines and randomized, controlled trials confirm the effectiveness of lactulose in the treatment of subclinical hepatic encephalopathy. If diarrhea develops, the drug should be stopped and reinstituted at a lower dose.


Patients requiring a low galactose diet

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]).

Subclinical (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.

Portal systemic encephalopathy (PSE), prevention: Oral:

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

Constipation (off-label dose): Infants, Children, and Adolescents: Oral: 1 to 2 g/kg/day (1.5 to 3 mL/kg/day) once daily or in 2 divided doses (NASPGHAN [Tabbers 2014]); maximum daily dose: 60 mL/day in adults.

Dosing: Renal Impairment

There are no dosage adjustments provided in the manufacturer’s labeling.

Dosing: Hepatic Impairment

There are no dosage adjustments provided in the manufacturer’s labeling.


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

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

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience burping, abdominal cramps, flatulence, vomiting, or nausea. Have patient report immediately to prescriber signs of high blood sugar (confusion, fatigue, increased thirst, increased hunger, polyuria, flushing, fast breathing, or breath that smells like fruit) or diarrhea (HCAHPS).

• Educate patient about signs of a significant reaction (eg, 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. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.