Trade Name(s)

  • Constulose
  • Enulose
  • Generlac
  • Kristalose

Ther. Class.


Pharm. Class.



  • Chronic constipation.
  • Adjunct in the management of portal-systemic (hepatic) encephalopathy.


  • Increases water content and softens the stool.
  • Lowers the pH of the colon, which inhibits the diffusion of ammonia from the colon into the blood, thereby reducing blood ammonia levels.

Therapeutic Effect(s):

  • Relief of constipation.
  • Decreased blood ammonia levels with improved mental status in portal-systemic encephalopathy.


Absorption: Less than 3% absorbed after oral administration.

Distribution: Unknown.

Metabolism and Excretion: Absorbed lactulose is excreted unchanged in the urine. Unabsorbed lactulose is metabolized by colonic bacteria to lactic, acetic, and formic acids.

Half-life: Unknown.

TIME/ACTION PROFILE (relief of constipation)

PO24–48 hrunknownunknown


Contraindicated in:

  • Patients on low-galactose diets.

Use Cautiously in:

  • Diabetes mellitus;
  • Excessive or prolonged use (may lead to dependence);
  • Lactation:  Safety not established in breastfeeding.

Adverse Reactions/Side Effects

Endo: hyperglycemia (patients with diabetes)

GI: belching, cramps, distention, flatulence, diarrhea

* CAPITALS indicate life-threatening.
Underline indicate most frequent.



  • Should not be used with other  laxatives  in the treatment of hepatic encephalopathy (leads to inability to determine optimal dose of lactulose).
  •  Anti-infectives  may ↓ effectiveness in treatment of hepatic encephalopathy.



PO (Adults): 15–30 mL/day up to 60 mL/day as liquid or 10–20 g as powder for oral solution (up to 40 g/day has been used).

PO (Children): 7.5 mL once daily after breakfast (unlabeled).

Portal-Systemic Encephalopathy

PO (Adults): 30–45 mL 3–4 times/day; may be given every 1–2 hr initially to induce laxation.

PO Infants: 2.5–10 mL/day in 3–4 divided doses (unlabeled).

PO (Children  and Adolescents): 40–90 mL/day in 3–4 divided doses (unlabeled).

Rect:  (Adults): 300 mL diluted and administered as a retention enema every 4–6 hr.

Availability (generic available)

Oral solution: 10 g/15 mL

Single-use packets (Kristalose): 10 g (equal to 15 mL liquid lactulose), 20 g (equal to 30 mL liquid lactulose)


  • Assess patient for abdominal distention, presence of bowel sounds, and normal pattern of bowel function.

    • Assess color, consistency, and amount of stool produced.
  • Portal-Systemic Encephalopathy: Assess mental status (orientation, level of consciousness) before and periodically throughout course of therapy.

Lab Test Considerations:

Should ↓ blood ammonia concentrations by 25–50%.

  • May cause ↑ blood glucose levels in patients with diabetes.
  • Monitor serum electrolytes periodically when used chronically. May cause diarrhea with resulting hypokalemia and hypernatremia.


  • When used in hepatic encephalopathy, adjust dose until patient averages 2–3 soft bowel movements per day. During initial therapy, 30–45 mL may be given hourly to induce rapid laxation.

    • Darkening of solution does not alter potency.
  • PO Mix with fruit juice, water, milk, or carbonated citrus beverage to improve flavor. Administer with a full glass (240 mL) of water or juice. May be administered on an empty stomach for more rapid results.
    • Dissolve single dose packets (Kristalose) in 4 oz of water. Solution should be colorless to slightly pale yellow.
  • Rect:  To administer enema, use rectal balloon catheter. Mix 300 mL of lactulose with 700 mL of water or 0.9% NaCl. Enema should be retained for 30–60 min. If inadvertently evacuated, may repeat administration.

Patient/Family Teaching

  • Explain purpose of lactulose to patient. Instruct patient to take lactulose as directed.
  • Encourage patients to use other forms of bowel regulation, such as increasing bulk in the diet, increasing fluid intake, and increasing mobility. Normal bowel habits are individualized and may vary from 3 times/day to 3 times/wk.
  • Caution patients that this medication may cause belching, flatulence, or abdominal cramping. Health care professional should be notified if this becomes bothersome or if diarrhea occurs.
  • Rep:  Advise females of reproductive potential to notify health care professional if pregnancy is planned or suspected or if breastfeeding.

Evaluation/Desired Outcomes

  • Passage of a soft, formed bowel movement, usually within 24–48 hr.
  • Clearing of confusion, apathy, and irritation, and improved mental status in portal-systemic encephalopathy. Improvement may occur within 2 hr after enema and 24–48 hr after oral administration.