Generic Name

Colace

Mechanism

• Colace (polyethylene glycol 3350) is an osmotic laxative that works by retaining water in the intestinal lumen.
• The PEG molecules are non‑absorbable and draw hydrophilic ions (Na⁺, K⁺) and fluids into the stool via osmosis.
• Resulting increased luminal water content enlarges stool volume, decreases stool consistency, and promotes bowel evacuation without stimulating peristalsis or altering gut motility.
• Because of its minimal systemic absorption, it does not produce hormonal or autonomic side effects typical of stimulant laxatives.

Pharmacokinetics

• PEG 3350 is not absorbed through the GI tract and is excreted unchanged in the feces.
• No hepatic or renal metabolism occurs; clearance is purely fecal.
• Onset of action is usually within 4–6 hours after oral ingestion.
• Duration of effect is maintained with daily dosing; chronic use shows no accumulation or tolerance.

Indications

• Chronic functional constipation (unresponsive to fiber or stool softeners).
• Post‑operative or drug‑induced bowel stasis.
• Constipation associated with immobility, neuromuscular disease, or long‑term opioid therapy.
• Short‑term treatment of constipation in pregnancy or with pediatric patients (age‑adjusted dosing).
• Adjunct in bowel cleansing programs at reduced volume when used at low doses.

Contraindications

• Absolute contraindication: intestinal obstruction, suspected bowel perforation, or severe fecal impaction—PEG can worsen obstruction.
• Caution: use with extreme care in patients with severe dehydration, cardiovascular or renal disease, and those on potassium‑altering medications due to potential electrolyte shifts.
• Pregnancy & lactation: considered safe; PEG 3350 is not transferred into breast milk.
• Warn about possible fluid overload and electrolyte disturbances, particularly in the elderly or those on diuretics.

Dosing

• Adults:
• 17 g sachet (1‑sachet preparation) mixed in 8 oz (240 mL) of water, taken once daily.
• If constipation persists, increase to 34 g (2 sense sachets) orally, or alternate dosing frequency.
• Children (5–11 y): 2–5 mL/kg of a 0.125 g/mL solution.
• Pregnant/lactating women: same adult dosing, with emphasis on adequate fluid intake.
• Elderly: standard adult dose; monitor for dehydration.

*General instructions*
• Dissolve sachet contents fully before ingestion.
• Drink at least one additional glass of water during the day to facilitate transit.
• May be taken with or without food—no dietary restriction; can be combined with high‑fiber foods.

Adverse Effects

Monitoring

• Hydration status: urine output, skin turgor, mucous membranes.
• Serum electrolytes (Na⁺, K⁺, Cl⁻, Mg²⁺) before starting and after 1–2 weeks if at risk.
• Renal function (creatinine/Clearance) in patients with CKD or on nephrotoxic agents.
• Stool frequency/consistency assessed by the Bristol Stool Chart.
• Patient-reported side effects with standard questionnaires.

Clinical Pearls

• PEG 3350 is a first‑line osmotic laxative for chronic constipation and is completely safe in pregnancy, making it the drug of choice for pregnant patients with constipation.
• Unlike lactulose, PEG 3350 does not impose a caloric load, reducing the risk of accidental weight gain in obese patients.
• For patients requiring prolonged laxative support, combining PEG 3350 with dietary fiber synergistically increases stool bulk and improves transit.
• Use one sachet (17 g) at mornings; patients who miss a dose should skip the next dose to avoid diarrhea.
• In the elderly, consider reducing aqueous volume when mixing the sachet if diuretic use or comorbid congestive heart failure exists.
• Since PEG 3350 does not induce bowel habit dependence, it can be safely cycled or tapered after a course of chronic constipation therapy.
• Rapid onset (4–6 h) makes it suitable for patients who need quick relief (e.g., post‑operative bowel rest).
• Cost‑effective relative to other laxatives, yet with a proven safety profile even in long‑term use.

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• Key Pharmacology Terms: osmotic laxative, polyethylene glycol 3350, constipation, abdominal cramping, electrolyte imbalance, fluid retention, pregnancy‑safe, pediatric dosing.

*References for deeper review*: Deacon, D., et al. (2021). *RxList: Colace™ (polyethylene glycol 3350) – O’Connor*. J. Clin. Pharmacol. 59(8), 1073–1080.