Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
GLYCOLAX vs CHRONULAC
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Osmotic laxative. Polyethylene glycol (PEG) increases intraluminal water volume in the colon by osmosis, promoting stool passage and relieving constipation.
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.
Treatment of occasional constipation
Treatment of constipation,Hepatic encephalopathy (portal-systemic encephalopathy)
17 g (1 heaping tablespoon) dissolved in 4-8 ounces of liquid once daily, orally.
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; local colonic transit time approximately 2-4 hours.
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.
Not metabolized; excreted unchanged in feces.
Not absorbed systemically; metabolized by colonic bacteria (e.g., Lactobacillus, Bacteroides) to lactic acid, acetic acid, and other short-chain fatty acids.
Minimally absorbed; excreted primarily unchanged in feces via osmotic action. Renal excretion negligible (<0.2% absorbed dose).
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.
Not bound (polyethylene glycol not bound to plasma proteins).
Negligible (<5%), primarily to albumin.
Not applicable due to minimal absorption; if absorbed, distributes largely in extracellular fluid; Vd negligible.
Approximately 0.25 L/kg; distributes mainly into extracellular fluid.
Oral: <0.2% (systemic absorption negligible); rectal: minimal systemic absorption.
Oral: poorly absorbed; <3% reaches systemic circulation as intact lactulose; the remainder is metabolized by colonic bacteria.
No dose adjustment required, but use with caution in patients with renal impairment due to risk of electrolyte disturbances.
No dose adjustment required for renal impairment; caution in severe renal impairment due to electrolyte disturbances.
No dose adjustment required; use standard dosing for patients with hepatic impairment.
No adjustment needed; used in hepatic encephalopathy at higher doses.
For children 2-11 years: 8.5 g (1/2 heaping tablespoon) dissolved in 4-8 ounces of liquid once daily; for children 12 years and older: same as adult dosing.
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.
Use with caution due to increased risk of electrolyte disturbances and dehydration; consider lower starting dose (e.g., 8.5 g once daily) and monitor electrolytes and fluid status.
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 beyond 1 week may cause dependence; caution in patients with bowel obstruction, ileus, or gastrointestinal perforation; risk of electrolyte disturbances with prolonged use.
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)
Bowel obstruction, ileus, gastrointestinal perforation, toxic colitis, toxic megacolon, known hypersensitivity to PEG.
Patients with galactosemia,Intestinal obstruction,Known hypersensitivity to lactulose
No significant food interactions. May be taken with or without food. Avoid concurrent use with high-fiber foods if bloating occurs, as this may exacerbate symptoms.
No specific food interactions, but avoid concurrent use with other laxatives. Ensure adequate fluid intake to reduce risk of hypernatremia.
Polyethylene glycol 3350 (Glyco Lax) has no known teratogenic effects. Animal studies show no fetal harm. Human data are limited but no increased risk of major congenital malformations has been reported. Use in all trimesters is considered low risk.
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.
Polyethylene glycol 3350 is minimally absorbed systemically (<0.1%), making excretion into breast milk negligible. The M/P ratio is not defined due to lack of detection in plasma. Likely safe during breastfeeding.
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 is typically needed. Pharmacokinetic changes in pregnancy (e.g., increased plasma volume, altered GI motility) are unlikely to affect this non-absorbed agent. Standard adult doses (17 g once daily) remain appropriate.
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).
GLYCOLAX (polyethylene glycol 3350) is an osmotic laxative. Onset of action is 24-48 hours. Not for acute relief of constipation; use for chronic constipation. May take 2-4 days for full effect. Avoid in intestinal obstruction or perforation. Dose can be adjusted to achieve soft stools. Can be mixed with any non-carbonated beverage.
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 once daily, preferably in the morning, mixed in 4-8 ounces of liquid.,Effect may take 2-4 days; do not use for immediate relief.,Do not exceed 7 days of use without consulting a doctor.,Drink plenty of fluids while using this medication.,Notify your doctor if you have severe stomach pain, nausea, vomiting, or if you notice blood in your stool.,Keep out of reach of children.
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 GLYCOLAX vs CHRONULAC, answered by our medical review team.
GLYCOLAX is a Osmotic Laxative that works by Osmotic laxative. Polyethylene glycol (PEG) increases intraluminal water volume in the colon by osmosis, promoting stool passage and relieving constipation.. 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 GLYCOLAX 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 GLYCOLAX is: 17 g (1 heaping tablespoon) dissolved in 4-8 ounces of liquid once daily, orally.. 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 GLYCOLAX 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. GLYCOLAX is classified as Category C. Polyethylene glycol 3350 (GlycoLax) has no known teratogenic effects. Animal studies show no fetal harm. Human data are limited but no increased risk of major congenital malformati. 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.