Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
MIRALAX vs CHRONULAC
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Polyethylene glycol 3350 (PEG 3350) is an osmotic laxative that works by retaining water in the stool through hydrogen bonding, increasing fecal water content and promoting bowel movements.
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,Bowel preparation before colonoscopy (off-label)
Treatment of constipation,Hepatic encephalopathy (portal-systemic encephalopathy)
17 g (1 heaping tablespoon) dissolved in 4–8 oz of water, juice, soda, coffee, or tea, administered orally once daily. Maximum duration of use: 7 days.
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; polyethylene glycol 3350 is minimally absorbed and systemic half-life is not clinically relevant.
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.
PEG 3350 is not metabolized; it is 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.
Primarily excreted unchanged in feces (>90% of oral dose); negligible renal elimination (<0.1% recovered in urine).
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.
Minimal to no protein binding due to negligible systemic absorption.
Negligible (<5%), primarily to albumin.
Not applicable due to negligible absorption; localized to gastrointestinal tract.
Approximately 0.25 L/kg; distributes mainly into extracellular fluid.
Negligible oral bioavailability (less than 0.01%) as the drug is not absorbed from the gastrointestinal tract.
Oral: poorly absorbed; <3% reaches systemic circulation as intact lactulose; the remainder is metabolized by colonic bacteria.
No dosage adjustment required for mild to moderate renal impairment (GFR 30–89 m L/min). For severe renal impairment (GFR <30 m L/min) or dialysis-dependent patients, use with caution due to potential for electrolyte disturbances; consider reduced starting dose (e.g., 8.5 g daily) and monitor for adverse effects.
No dose adjustment required for renal impairment; caution in severe renal impairment due to electrolyte disturbances.
No specific guidelines for Child-Pugh classification. Use with caution in severe hepatic impairment due to potential for altered fluid and electrolyte balance. No dose adjustment recommended but clinical monitoring advised.
No adjustment needed; used in hepatic encephalopathy at higher doses.
Children 6 months to <1 year: 4.25 g (1/4 packet) once daily. Children 1 to <6 years: 8.5 g (1/2 packet) once daily. Children 6 to <12 years: 17 g (1 packet) once daily. Dissolve in 4–8 oz of liquid. Maximum duration: 7 days. Not recommended for children <6 months.
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.
No specific dose adjustment. Use with caution in patients >65 years due to increased risk of electrolyte imbalance and dehydration. Consider initiating with lower doses (e.g., 8.5 g daily) and ensure adequate fluid intake. Monitor for adverse effects, particularly if using for more than a few days.
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 for constipation lasting more than 2 weeks may indicate a serious condition; consider further evaluation.,Do not use if experiencing nausea, vomiting, abdominal pain, or a sudden change in bowel habits lasting more than 2 weeks.,Allergic reactions including urticaria and rash have been reported.,Risk of electrolyte disturbances with prolonged use or in patients with renal impairment.
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)
Known hypersensitivity to polyethylene glycol or any component of the formulation,Bowel obstruction or perforation,Toxic colitis or megacolon,Gastrointestinal obstruction or ileus
Patients with galactosemia,Intestinal obstruction,Known hypersensitivity to lactulose
None significant. Mira LAX can be mixed with any food or beverage without affecting absorption or efficacy. However, avoid concurrent use with high-fiber supplements or bulk-forming laxatives to prevent excessive stool volume or gas.
No specific food interactions, but avoid concurrent use with other laxatives. Ensure adequate fluid intake to reduce risk of hypernatremia.
MIRALAX (polyethylene glycol 3350) is considered non-teratogenic based on animal studies and human data. No increased risk of congenital malformations has been reported. Risk in all trimesters is minimal due to negligible systemic absorption.
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 not absorbed systemically following oral administration, thus it is not expected to be excreted into breast milk. M/P ratio is not applicable. Considered compatible with 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 required during pregnancy. Pharmacokinetics are not significantly altered due to minimal absorption. Standard adult dosing (17 g powder dissolved in 4-8 oz water) is recommended.
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).
Mira LAX (polyethylene glycol 3350) is an osmotic laxative that works by drawing water into the bowel, softening stool and increasing frequency of movements. Onset of action is 24-48 hours. It is not absorbed systemically, making it safe for most patients, including those with renal impairment. Avoid in bowel obstruction or perforation. For chronic constipation, titrate dose gradually to avoid bloating. Can be mixed with any beverage (hot or cold) for improved compliance.
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.
Mix one dose (17g) in 4-8 ounces of liquid (water, juice, coffee, soda) and drink immediately. Do not use with starch-thickened liquids.,Do not exceed 7 days of treatment for acute constipation unless directed by a doctor.,May take 24-48 hours to produce a bowel movement. Do not use if you have abdominal pain, nausea, or vomiting.,Store at room temperature. Do not freeze.,Notify your doctor if you experience rectal bleeding or no bowel movement after 7 days.
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 MIRALAX vs CHRONULAC, answered by our medical review team.
MIRALAX is a Osmotic Laxative that works by Polyethylene glycol 3350 (PEG 3350) is an osmotic laxative that works by retaining water in the stool through hydrogen bonding, increasing fecal water content and promoting bowel movements.. 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 MIRALAX 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 MIRALAX is: 17 g (1 heaping tablespoon) dissolved in 4–8 oz of water, juice, soda, coffee, or tea, administered orally once daily. Maximum duration of use: 7 days.. 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 MIRALAX 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. MIRALAX is classified as Category C. MIRALAX (polyethylene glycol 3350) is considered non-teratogenic based on animal studies and human data. No increased risk of congenital malformations has been reported. Risk in al. 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.