Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CONSTILAC vs CHRONULAC
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Constilac (lactulose) is a synthetic disaccharide that is not absorbed in the small intestine. In the colon, it is metabolized by bacteria to short-chain fatty acids (e.g., lactic acid), which osmotically draw water into the bowel, producing a laxative effect. Additionally, in hepatic encephalopathy, the acidification of colonic contents traps ammonia (NH3) as ammonium (NH4+), reducing its absorption.
Lactulose is a synthetic disaccharide that is not absorbed in the small intestine. It is hydrolyzed by colonic bacteria to form low molecular weight acids (mainly lactic and acetic acid), which osmotically draw water into the colon, softening stools and increasing stool frequency. Additionally, lactulose decreases colonic p H, which traps ammonia (NH3) as ammonium (NH4+), reducing serum ammonia levels.
Constipation (FDA-approved),Portal-systemic encephalopathy (hepatic encephalopathy) (FDA-approved)
Treatment of constipation,Hepatic encephalopathy (portal-systemic encephalopathy)
Oral, 15-45 m L (10-20 g lactulose) once daily, titrated to produce 2-3 soft stools daily; may be given as a single dose or divided twice daily. Onset of action 24-48 hours.
10-30 m L orally once daily to twice daily; for acute constipation, 20-30 m L initially; for hepatic encephalopathy, 30-60 m L every 1-2 hours to achieve 2-3 soft stools daily.
Not applicable due to negligible systemic absorption; lactulose acts locally in the colon.
Terminal elimination half-life approximately 1.5-2.5 hours in adults with normal renal function; may be prolonged to 4-8 hours in patients with renal impairment.
Lactulose is not absorbed in the small intestine. It undergoes bacterial metabolism in the colon to lactic acid, acetic acid, and other short-chain fatty acids.
Not absorbed systemically; metabolized by colonic bacteria (e.g., Lactobacillus, Bacteroides) to lactic acid, acetic acid, and other short-chain fatty acids.
Primarily fecal as unchanged drug (systemic absorption negligible). Renal excretion accounts for <2% of any absorbed fraction. Biliary excretion is minimal.
Primarily renal (as unchanged drug and metabolites): ~40-50% of dose excreted in urine within 24 hours; biliary/fecal elimination accounts for the remainder, with approximately 2-5% recovered in feces as parent compound.
Negligible (<1%) due to minimal systemic absorption.
Negligible (<5%), primarily to albumin.
Not applicable (negligible systemic distribution).
Approximately 0.25 L/kg; distributes mainly into extracellular fluid.
Oral: <2% (largely unabsorbed; metabolized by colonic bacteria).
Oral: poorly absorbed; <3% reaches systemic circulation as intact lactulose; the remainder is metabolized by colonic bacteria.
No dose adjustment required for renal impairment. Lactulose is minimally absorbed and renally excreted unchanged; safety established in all stages of chronic kidney disease.
No dose adjustment required for renal impairment; caution in severe renal impairment due to electrolyte disturbances.
Contraindicated in Child-Pugh class C cirrhosis due to risk of hepatic encephalopathy exacerbation from colonic acidification. In Child-Pugh A and B, standard dosing may be used with caution; monitor for electrolyte disturbances and volume status.
No adjustment needed; used in hepatic encephalopathy at higher doses.
Infants: 2.5-10 m L/day in divided doses. Children 1-5 years: 5-15 m L/day. Children 6-12 years: 15-30 m L/day. Adolescents: 15-45 m L/day. Administer orally; adjust to produce soft stools.
Infants: 2.5-5 m L orally once daily; Children 1-5 years: 5-10 m L once daily; Children 6-12 years: 10-15 m L once daily; Adolescents: 15-30 m L once daily; adjust based on response.
Initiate at lower end of adult dose (15 m L once daily) and titrate slowly to avoid diarrhea and electrolyte imbalances. Monitor for dehydration, hypokalemia, and hypernatremia, especially in patients with renal impairment or on diuretics.
Start at low end of dosing range (10-15 m L once daily) due to increased risk of electrolyte imbalance and dehydration; monitor fluid/electrolyte status.
None
None.
Use with caution in patients with diabetes mellitus (lactulose may contain small amounts of galactose and lactose),Electrolyte disturbances (particularly hypokalemia and hypernatremia) may occur with prolonged use,Risk of galactosemia in patients with galactose intolerance,May cause abdominal discomfort, flatulence, and diarrhea
Electrolyte disturbances (e.g., hypernatremia, hypokalemia) with prolonged use or high doses,Diarrhea may cause fluid and electrolyte loss,Risk of colonic distention or fecal impaction,Use caution in patients with galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption (contains galactose and lactose)
Patients with galactosemia,Intestinal obstruction or suspected obstruction,Undiagnosed abdominal pain
Patients with galactosemia,Intestinal obstruction,Known hypersensitivity to lactulose
No significant food interactions. May be mixed with juice or water to mask taste. Avoid excessive intake of dairy products if lactose intolerant, as lactulose is derived from lactose.
No specific food interactions, but avoid concurrent use with other laxatives. Ensure adequate fluid intake to reduce risk of hypernatremia.
No known teratogenic effects. Lactulose is not absorbed systemically; no fetal risk expected in any trimester.
Lactulose (CHRONULAC) is not absorbed systemically; no teratogenic effects are expected. No adequate and well-controlled studies in pregnant women; animal reproduction studies not conducted. Based on lack of systemic absorption, risk to fetus is low across all trimesters.
Considered safe during breastfeeding. M/P ratio not applicable as lactulose is not absorbed; no significant excretion into breast milk expected.
Lactulose is not absorbed orally; therefore, excretion into breast milk is negligible. Considered compatible with breastfeeding; no M/P ratio available due to lack of systemic absorption.
No dose adjustment required. Pharmacokinetics unchanged due to lack of systemic absorption.
No dose adjustment required during pregnancy. Pharmacokinetics of lactulose are unchanged due to lack of systemic absorption. Use standard dosing for constipation (15-30 m L daily, titrated to effect).
CONSTILAC (lactulose) is a non-absorbable disaccharide that acts as an osmotic laxative. It is also used off-label for hepatic encephalopathy by reducing serum ammonia. Onset of action for constipation is 24-48 hours. Overuse can cause electrolyte disturbances, particularly hypernatremia and hypokalemia. In hepatic encephalopathy, titrate to 2-3 soft stools per day.
Chronulac (lactulose) is a non-absorbable disaccharide used for constipation and hepatic encephalopathy. Onset of action for constipation is 24-48 hours; monitor for electrolyte disturbances (hypernatremia) with prolonged use. Do not use with other laxatives in acute abdomen. For hepatic encephalopathy, titrate to 2-3 soft stools daily.
Take exactly as prescribed; effects may take 1-2 days.,May cause flatulence and cramping initially.,Mix with fruit juice or water to improve taste.,If symptoms persist beyond 1 week, consult your doctor.,Do not use if you have galactosemia or bowel obstruction.
May take 24-48 hours to produce a bowel movement; do not use if you have abdominal pain, nausea, or vomiting.,Mix with fruit juice, milk, or water to improve taste.,Store at room temperature; do not freeze.,Report excessive diarrhea or electrolyte imbalance symptoms (muscle cramps, weakness).
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about CONSTILAC vs CHRONULAC, answered by our medical review team.
CONSTILAC is a Osmotic Laxative that works by Constilac (lactulose) is a synthetic disaccharide that is not absorbed in the small intestine. In the colon, it is metabolized by bacteria to short-chain fatty acids (e.g., lactic acid), which osmotically draw water into the bowel, producing a laxative effect. Additionally, in hepatic encephalopathy, the acidification of colonic contents traps ammonia (NH3) as ammonium (NH4+), reducing its absorption.. CHRONULAC is a Osmotic Laxative that works by Lactulose is a synthetic disaccharide that is not absorbed in the small intestine. It is hydrolyzed by colonic bacteria to form low molecular weight acids (mainly lactic and acetic acid), which osmotically draw water into the colon, softening stools and increasing stool frequency. Additionally, lactulose decreases colonic p H, which traps ammonia (NH3) as ammonium (NH4+), reducing serum ammonia levels.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CONSTILAC and CHRONULAC depend on the specific clinical indication. These are both Osmotic Laxative agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of CONSTILAC is: Oral, 15-45 m L (10-20 g lactulose) once daily, titrated to produce 2-3 soft stools daily; may be given as a single dose or divided twice daily. Onset of action 24-48 hours.. The standard adult dose of CHRONULAC is: 10-30 m L orally once daily to twice daily; for acute constipation, 20-30 m L initially; for hepatic encephalopathy, 30-60 m L every 1-2 hours to achieve 2-3 soft stools daily.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between CONSTILAC and CHRONULAC in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. CONSTILAC is classified as Category C. No known teratogenic effects. Lactulose is not absorbed systemically; no fetal risk expected in any trimester.. CHRONULAC is classified as Category C. Lactulose (CHRONULAC) is not absorbed systemically; no teratogenic effects are expected. No adequate and well-controlled studies in pregnant women; animal reproduction studies not . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.