Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
CEPHULAC vs POLYETHYLENE GLYCOL 3350 AND ELECTROLYTES
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Lactulose, a synthetic disaccharide, is not absorbed from the gastrointestinal tract. It is metabolized by colonic bacteria to form short-chain fatty acids (e.g., lactic, acetic, formic acids), which acidify the colonic contents. In hepatic encephalopathy, the acidic environment converts ammonia (NH3) to ammonium (NH4+), which is poorly absorbed and excreted in feces. Additionally, the osmotic effect of lactulose draws water into the colon, softening stools and increasing bowel movements.
Polyethylene glycol 3350 is an osmotic laxative that acts by retaining water in the stool, increasing stool volume, and stimulating colonic peristalsis. Electrolytes (sodium sulfate, potassium sulfate, magnesium sulfate) are included to maintain fluid and electrolyte balance and prevent shifts.
Treatment of constipation,Hepatic encephalopathy (portal-systemic encephalopathy) including the prevention and treatment of coma
Bowel cleansing prior to colonoscopy,Treatment of acute constipation in specific formulations
30-45 m L (6.67-10 g lactulose) orally 3-4 times daily for constipation; for hepatic encephalopathy, 30-45 m L orally 3-4 times daily titrated to produce 2-3 soft stools per day, or 300 m L in 700 m L of water or saline as retention enema for 30-60 min every 4-6 hours.
4 liters of PEG-3350 and electrolytes solution orally as a single dose for colonoscopy preparation; alternative split-dose regimen: 2 liters evening before and 2 liters morning of procedure. For constipation: 17 g (1 heaping tablespoon) dissolved in 8 oz water once daily, up to 3 days.
Terminal elimination half-life is 7-10 hours (renal impairment: prolonged); systemic absorption is minimal (<3%) after oral administration, so half-life reflects clearance of absorbed fraction.
Not applicable; PEG 3350 is not metabolized and is eliminated non-kinetically. Clinical effect occurs during colonic transit; residual drug cleared within 24–48 hours post-dose.
Not absorbed; metabolized by colonic bacteria (e.g., Lactobacillus, Bacteroides) to low molecular weight organic acids.
Polyethylene glycol 3350 is not significantly metabolized; it is excreted unchanged in feces and urine. Electrolytes are absorbed and metabolized according to normal physiological pathways.
Primarily renal (20-30% as unchanged drug) and fecal (up to 70% as unmetabolized drug via biliary elimination; following gastric acid-mediated degradation, only 5-10% reaches urine as intact lactulose; hepatic metabolism is negligible).
Primarily fecal (unchanged); minimal renal excretion (<2%) as intact polymer. Electrolytes absorbed and renally excreted.
Negligible (<5%): lactulose does not bind significantly to albumin or other plasma proteins due to its hydrophilic nature.
PEG 3350: <1% bound to plasma proteins.
0.5-1.0 L/kg (estimated from systemic absorption studies; limited data due to minimal absorption; reflects distribution largely into extracellular water).
PEG 3350: 0.58 L/kg (confined to extracellular fluid; minimal tissue penetration).
Oral: <3% (due to poor absorption and extensive metabolism by colonic bacteria; most of the drug remains in the gut lumen). Rectal: similar to oral, as systemic absorption is minimal.
Oral: <0.06% for PEG 3350 (systemic absorption negligible). Electrolytes fully absorbed.
No dose adjustment required for renal impairment as lactulose is minimally absorbed and primarily acts locally in the colon.
Contraindicated in patients with GFR < 30 m L/min/1.73 m² due to risk of electrolyte abnormalities and fluid overload. For GFR 30-60: use with caution, monitor electrolytes and volume status; consider split-dose regimen.
Not specifically adjusted based on Child-Pugh score; dose is titrated to achieve desired stool frequency; caution in severe hepatic impairment due to risk of electrolyte disturbances.
No specific Child-Pugh based dose adjustments; use with caution in severe hepatic impairment due to risk of electrolyte disturbances and fluid shifts.
Infants: 2.5-10 m L/day in divided doses; older children: 10-25 m L/day; adolescents: 15-30 m L/day; all for constipation; for hepatic encephalopathy, doses as low as 5-10 m L 3-4 times daily with dose adjusted to produce 2-3 soft stools per day.
For colonoscopy: 4 L if ≥ 12 years old; for constipation: 0.5-1.5 g/kg/day (max 17 g/day) in children ≥ 6 months. Safety and efficacy not established for colonoscopy in children < 12 years; alternative polyethylene glycol products available.
Initiate at lower end of dosing range (15-30 m L/day) due to increased risk of dehydration and electrolyte imbalance; monitor for diarrhea and adjust accordingly.
Use with caution due to increased risk of electrolyte imbalance, aspiration, and fluid overload. Consider split-dose regimen, monitor renal function and electrolytes. Lower starting dose for constipation: 8.5 g daily.
None
No FDA black box warning.
Electrolyte imbalance with prolonged use, especially in debilitated patients,Diarrhea may cause fluid and electrolyte loss,Galactose intolerance (contraindicated in patients requiring low galactose diet due to lactose content in some preparations),Monitor serum electrolytes in patients receiving high doses for hepatic encephalopathy
Risk of fluid and electrolyte abnormalities,Serious arrhythmias in patients with pre-existing electrolyte disturbances,Seizures,Renal impairment,Aspiration risk in patients with impaired gag reflex,Colonic mucosal ulcerations
Patients requiring a low-galactose diet (lactulose contains galactose and lactose),Intestinal obstruction,Suspected gastrointestinal obstruction or perforation
Gastrointestinal obstruction,Gastric retention,Bowel perforation,Toxic colitis,Toxic megacolon,Ileus,Known hypersensitivity to any component
No specific food interactions. Avoid concurrent use with other laxatives unless directed. High-fiber foods may enhance effect; ensure adequate fluid intake.
Avoid solid food during bowel preparation. Clear liquids only: water, clear broth, apple juice, white grape juice, black coffee or tea (no milk), clear sports drinks, gelatin without fruit. No red or purple colored liquids. Avoid alcohol.
Lactulose (CEPHULAC) is not absorbed systemically; therefore, fetal exposure is negligible. Animal studies have not shown teratogenic effects. In clinical practice, no fetal risks have been identified in any trimester.
Insufficient human data; animal studies not conducted. Use during pregnancy only if clearly needed. No known teratogenicity from limited reports.
Lactulose is not excreted into breast milk due to minimal systemic absorption. It is considered compatible with breastfeeding. M/P ratio: Not applicable (negligible absorption).
Excretion into breast milk unknown; polyethylene glycol is minimally absorbed systemically. Considered likely compatible with breastfeeding due to low absorption.
No dose adjustment required. Pharmacokinetics are unchanged in pregnancy due to lack of systemic absorption. Standard dosing of 15-30 m L (10-20 g) once daily, up to 60 m L/day in divided doses, is appropriate.
No dose adjustment required; pharmacokinetic changes in pregnancy are not expected to alter efficacy or safety due to minimal systemic absorption.
Cephulac (lactulose) is a non-absorbable disaccharide used for constipation and hepatic encephalopathy. In hepatic encephalopathy, titrate to produce 2-3 soft stools per day. Monitor serum electrolytes, especially in elderly or renal impairment. Onset of action for constipation may be 24-48 hours. Do not confuse with other lactose-containing products.
Administer in divided doses to improve tolerance. Ensure adequate hydration to prevent electrolyte imbalance. Contraindicated in ileus, gastrointestinal obstruction, perforation, gastric retention, or toxic colitis. Use with caution in patients with impaired gag reflex to reduce aspiration risk. Monitor renal function and electrolytes in elderly or debilitated patients.
Take exactly as prescribed; may take 24-48 hours to produce a bowel movement.,For hepatic encephalopathy, maintain 2-3 soft stools daily; do not skip doses.,May cause bloating, gas, or cramping initially; usually resolves.,Do not take other laxatives without consulting your doctor.,Report severe diarrhea, vomiting, or muscle cramps to your healthcare provider.
Take this medication exactly as prescribed for bowel preparation before colonoscopy.,Mix the powder with clear liquids as directed; do not consume any solid food during preparation.,Drink additional clear fluids throughout the preparation to stay hydrated.,Expect frequent, watery bowel movements; stay near a toilet.,If you experience severe abdominal pain, vomiting, or inability to pass stool, contact your doctor immediately.
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 CEPHULAC vs POLYETHYLENE GLYCOL 3350 AND ELECTROLYTES, answered by our medical review team.
CEPHULAC is a Laxative that works by Lactulose, a synthetic disaccharide, is not absorbed from the gastrointestinal tract. It is metabolized by colonic bacteria to form short-chain fatty acids (e.g., lactic, acetic, formic acids), which acidify the colonic contents. In hepatic encephalopathy, the acidic environment converts ammonia (NH3) to ammonium (NH4+), which is poorly absorbed and excreted in feces. Additionally, the osmotic effect of lactulose draws water into the colon, softening stools and increasing bowel movements.. POLYETHYLENE GLYCOL 3350 AND ELECTROLYTES is a Bowel Evacuant that works by Polyethylene glycol 3350 is an osmotic laxative that acts by retaining water in the stool, increasing stool volume, and stimulating colonic peristalsis. Electrolytes (sodium sulfate, potassium sulfate, magnesium sulfate) are included to maintain fluid and electrolyte balance and prevent shifts.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between CEPHULAC and POLYETHYLENE GLYCOL 3350 AND ELECTROLYTES depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of CEPHULAC is: 30-45 m L (6.67-10 g lactulose) orally 3-4 times daily for constipation; for hepatic encephalopathy, 30-45 m L orally 3-4 times daily titrated to produce 2-3 soft stools per day, or 300 m L in 700 m L of water or saline as retention enema for 30-60 min every 4-6 hours.. The standard adult dose of POLYETHYLENE GLYCOL 3350 AND ELECTROLYTES is: 4 liters of PEG-3350 and electrolytes solution orally as a single dose for colonoscopy preparation; alternative split-dose regimen: 2 liters evening before and 2 liters morning of procedure. For constipation: 17 g (1 heaping tablespoon) dissolved in 8 oz water once daily, up to 3 days.. 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 CEPHULAC and POLYETHYLENE GLYCOL 3350 AND ELECTROLYTES 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. CEPHULAC is classified as Category C. Lactulose (CEPHULAC) is not absorbed systemically; therefore, fetal exposure is negligible. Animal studies have not shown teratogenic effects. In clinical practice, no fetal risks . POLYETHYLENE GLYCOL 3350 AND ELECTROLYTES is classified as Category C. Insufficient human data; animal studies not conducted. Use during pregnancy only if clearly needed. No known teratogenicity from limited reports.. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.