Generic Name

Polyethylene glycol 3350

Mechanism

Polyethylene glycol 3350 (PEG‑3350) is a non‑absorbable, high‑molecular‑weight polymer that functions as an osmotic laxative.
• PEG draws water from the intestinal lumen by *osmotic gradient*, increasing the water content and bulk of the stool.
• The increased stool mass activates mechanoreceptors along the colon, stimulating peristaltic reflexes and accelerating transit time.
• No systemic absorption occurs; the drug remains within the GI tract, minimizing systemic drug interactions.

Pharmacokinetics

• Absorption: Negligible; <1% of a dose is absorbed, primarily via the large intestine.
• Distribution: Minimal; drug stays in the GI lumen.
• Metabolism: None; PEG is chemically inert.
• Elimination: Primarily by fecal routes; unchanged PEG passes from ingestion to excretion.
• Half‑life: Not applicable to systemic circulation; effectiveness is driven by continuous luminal presence.

Indications

• Chronic constipation (primary or secondary).
• Analgesic‑induced constipation (e.g., opioid therapy).
• Pre‑operative bowel preparation for colonoscopy or abdominal surgery.
• Short‑term treatment of functional bloating and mild fecal impaction.
• Adjunctive therapy in irritable bowel syndrome with constipation (IBS‑C) when no other laxatives are effective.

Contraindications

• Absolute Contraindications:
• Mechanical bowel obstruction, paralytic ileus, or gross intestinal obstruction.
• Severe gastroparesis at the time of dosing.
• Warnings:
• Use cautiously in patients with chronic kidney disease (CKD) stages 4–5 or on dialysis: monitor serum electrolytes.
• Risk of dehydration; advise adequate oral fluid intake, especially in elderly or debilitated patients.
• Caution in patients on ACE inhibitors or ARBs; potential for hyperkalemia.
• Drug Interactions: No clinically significant interactions because of minimal absorption, but concomitant intestinal motility agents (like prokinetics) may alter response times.

Dosing

*Take doses with a full glass (200–300 ml) of water; patients should also increase total daily fluid intake (≥2 L).*

Adverse Effects

• Common:
• Abdominal cramping or discomfort
• Flatulence
• Bloating or mild nausea
• Diarrhea or loose stools
• Serious (Rare):
• Electrolyte disturbances: hyponatremia, hyperkalemia, hypomagnesemia (esp. in CKD).
• Dehydration, especially in geriatric or critically ill patients.
• Aspiration risk in patients with impaired swallowing.

Management:
• Monitor electrolytes in high‑risk patients.
• Re‑hydrate with oral or intravenous fluids as needed.
• For electrolyte imbalance, discontinue or adjust dose and treat underlying imbalance.

Monitoring

• Fluid Balance: Assess intake/output; ensure adequate hydration.
• Serum Electrolytes: Sodium, potassium, magnesium, especially in CKD, heart failure, or those on diuretics/ACEi/ARB.
• Renal Function: Serum creatinine/BUN in at-risk populations.
• Stool Frequency/Consistency: Use Bristol Stool Scale; documentation of improvement aids titration.
• Adverse Events: Document any severe abdominal pain, persistent diarrhea, or signs of obstruction.

Clinical Pearls

• Use the “PEGA‑FITS” mnemonic to remember patient selection: Patients with constipation, Elevated risk of iatrogenic dehydration, Geriatric, Aligned with Fluids, In patients on Treated with Supplemental electrolytes.
• Double‑sook dosing strategy: Some patients benefit from splitting the total daily dose into 2–3 administrations, especially in elderly or hypotensive patients, to reduce cramping and allow gradual colonic retention.
• Co‑administer electrolytes: In CKD or dialysis patients, regular oral potassium or magnesium supplementation can offset PEG‑induced losses.
• PEG in the ICU: Offers a non‑systemic laxative; can be administered via nasogastric tube when oral intake is limited.
• Avoid sodium‑loaded preparations (PEG‑3350 + sodium chloride) in patients at risk of hypernatremia; opt for potassium‑containing or isotonic formulations if needed.

*By adhering to these principles, healthcare professionals can effectively harness PEG‑3350 to alleviate constipation while minimizing potential complications.*