Cephulac, Chronulac
Classifications: hyperosmotic laxative;
Therapeutic: laxative, hyperosmotic

Pregnancy Category: B


10 g/15 mL solution, syrup


Reduces blood ammonia; appears to involve metabolism of lactose to organic acids by resident intestinal bacteria. Acidifies colon contents, which retards diffusion of nonionic ammonia (NH3) from colon to blood while promoting its migration from blood to colon. In the acidic colon, NH3 is converted to nonabsorbable ammonium ions (NH4+) and is then expelled in feces by laxative action.

Therapeutic Effect

Osmotic effect of organic acids causes laxative action, which moves water from plasma to intestines, softening stools, and stimulates peristalsis by pressure from water content of stool. Decreased blood ammonia in a patient with hepatic encephalopathy is marked by improved EEG patterns and mental state (clearing of confusion, apathy, and irritation).


Prevention and treatment of portal-systemic encephalopathy (PSE), including stages of hepatic precoma and coma, and by prescription for relief of chronic constipation.

Unlabeled Uses

to restore regular bowel habit posthemorrhoidectomy; to evacuate bowel in older adult patients with severe constipation after barium studies; and for treatment of chronic constipation in children.


Low galactose diet.

Cautious Use

Diabetes mellitus; concomitant use with electrocautery procedures (proctoscopy, colonoscopy); older adult and debilitated patients; pediatric use; pregnancy (category C); lactation.

Route & Dosage

Prevention and Treatment of Portal-Systemic Encephalopathy
Adult: PO 30–45 mL t.i.d. or q.i.d. adjusted to produce 2–3 soft stools/d
Adolescent/Child: PO 40–90 mL/d in divided doses adjusted to produce 2–3 soft stools/d
Infant: PO 2.5–10 mL/d in 3–4 divided doses adjusted to produce 2–3 soft stools/d

Management of Acute Portal-Systemic Encephalopathy
Adult: PO 30–45 mL q1–2 h until laxation is achieved, then adjusted to produce 2–3 soft stools/d. Rectal 300 mL diluted with 700 mL water given via rectal balloon catheter, and retained for 30–60 min, may repeat in 4–6 h if necessary or until patient can take PO

Chronic Constipation
Adult: PO 30–60 mL/d prn
Child: PO 7.5 mL/d after breakfast


  • Give with fruit juice, water, or milk (if not contraindicated) to increase palatability. Laxative effect is enhanced by taking with ample liquids. Avoid meal times.
  • Administer as a retention enema via a rectal balloon catheter. If solution is evacuated too soon, instillation may be promptly repeated.
  • Do not freeze. Avoid prolonged exposure to temperatures above 30° C (86° F) or to direct light. Normal darkening does not affect action, but discard solution that is very dark or cloudy.

Adverse Effects (≥1%)

GI: Flatulence, borborygmi, belching, abdominal cramps, pain, and distention (initial dose); diarrhea (excessive dose); nausea, vomiting, colon accumulation of hydrogen gas; hypernatremia.


Drug: laxatives may incorrectly suggest therapeutic action of lactulose.


Absorption: Poorly absorbed from GI tract. Metabolism: In gut by intestinal bacteria.

Nursing Implications

Assessment & Drug Effects

  • In children if the initial dose causes diarrhea, dosage is reduced immediately. Discontinue if diarrhea persists.
  • Promote fluid intake (≥1500–2000 mL/d) during drug therapy for constipation; older adults often self-limit liquids. Lactulose-induced osmotic changes in the bowel support intestinal water loss and potential hypernatremia. Discuss strategy with physician.

Patient & Family Education

  • Laxative action is not instituted until drug reaches the colon; therefore, about 24–48 h is needed.
  • Do not self-medicate with another laxative due to slow onset of drug action.
  • Notify physician if diarrhea (i.e., more than 2 or 3 soft stools/d) persists more than 24–48 h. Diarrhea is a sign of overdosage. Dose adjustment may be indicated.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2023 Last Updated On: 01/28/2023 (0)
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