MiraLAX (Polyethylene Glycol 3350)
polyethylene glycol 3350
Indications for Polyethylene Glycol 3350
| Indication | Approved Population | Therapy Type | Status |
|---|---|---|---|
| Occasional constipation | Adults & adolescents ≥17 years (OTC); adults (Rx) | Short-term symptomatic treatment (up to 7 days OTC; up to 2 weeks Rx) | FDA Approved |
Polyethylene glycol 3350 was first approved by the FDA as a prescription laxative in 1999 and became available over the counter in 2006. It is consistently ranked among the most commonly recommended laxatives by gastroenterologists and primary care providers due to its favourable safety profile, lack of systemic absorption, absence of habituation, and tolerability. Unlike stimulant laxatives, PEG 3350 does not alter colonic motility directly but works entirely through osmotic water retention in the stool.
Chronic idiopathic constipation (long-term use): Multiple RCTs support PEG 3350 for up to 6–12 months in chronic constipation, with sustained efficacy and safety. AGA and ACG guidelines recommend PEG as a first-line osmotic laxative for chronic constipation. (Evidence quality: high)
Pediatric constipation (<17 years): NASPGHAN/ESPGHAN guidelines recommend PEG 3350 as a first-line treatment for functional constipation in children. Typical dose: 0.2–0.8 g/kg/day (max 17 g/day). (Evidence quality: high)
Colonoscopy bowel preparation: 238 g PEG 3350 dissolved in 64 oz of a carbohydrate-electrolyte drink (e.g., Gatorade), given as a split dose. Not FDA-approved for this use; risk of electrolyte imbalance exists without balanced electrolyte solution. (Evidence quality: moderate)
Fecal impaction (disimpaction): Higher doses (1–1.5 g/kg/day for 3–6 days) used in pediatric and adult settings under medical supervision. (Evidence quality: moderate)
Dosing
Adult Dosing
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Occasional constipation — OTC self-medication | 17 g PO once daily | 17 g PO once daily | 17 g/day for up to 7 days | Dissolve in 120–240 mL (4–8 oz) of any beverage; bowel movement expected in 1–3 days Do not use starch-based thickeners; seek medical advice if no response after 7 days |
| Occasional/chronic constipation — prescription use | 17 g PO once daily | 17 g PO once daily | 17 g/day for up to 2 weeks | Physician may extend beyond 2 weeks for chronic constipation under monitoring 34 g/day studied in trials but associated with more diarrhea (DiPalma 2006) |
| Colonoscopy bowel preparation (off-label) | 238 g dissolved in 64 oz electrolyte drink | Split-dose regimen preferred | 238 g total | Consume as single or split dose (evening before + morning of procedure); often combined with bisacodyl 10–20 mg pre-treatment Not FDA-approved; risk of hyponatraemia without balanced electrolyte solution |
Pediatric Dosing (Off-Label — Under Medical Supervision)
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Functional constipation | 0.4 g/kg/day PO | 0.2–0.8 g/kg/day PO, titrated to effect | 17 g/day | NASPGHAN/ESPGHAN first-line recommendation; doses ≥0.8 g/kg/day associated with more GI adverse events Dissolve in age-appropriate volume of liquid |
| Fecal disimpaction | 1–1.5 g/kg/day PO for 3–6 days | Transition to maintenance (0.4 g/kg/day) after disimpaction | Per physician guidance | May be given as a single daily dose or divided; monitor for dehydration Alternative to enemas for initial disimpaction |
Unlike stimulant laxatives, PEG 3350 does not cause tachyphylaxis (loss of effectiveness with continued use). The FDA prescribing information explicitly states that no evidence of tachyphylaxis has been observed. This makes it suitable for long-term management of chronic constipation when used under medical supervision, though patients should also be counselled on dietary fibre, fluid intake, and exercise.
Pharmacology
Mechanism of Action
Polyethylene glycol 3350 is a high-molecular-weight, water-soluble, inert polymer that acts as a purely osmotic agent within the gastrointestinal lumen. PEG 3350 forms extensive hydrogen bonds with water molecules, preventing the normal reabsorption of water from the intestinal contents. This increases the osmotic pressure within the bowel lumen, resulting in water retention in the stool, softening of faecal consistency, and increased stool volume. The increased volume stimulates natural colonic peristalsis and accelerates transit. Crucially, PEG 3350 does not affect the active absorption or secretion of glucose or electrolytes across the intestinal mucosa. It is not fermented by colonic microflora (unlike lactulose), meaning it does not produce hydrogen or methane gas, which translates to less bloating and flatulence compared with other osmotic laxatives.
ADME Profile
| Parameter | Value | Clinical Implication |
|---|---|---|
| Absorption | Virtually none; systemic absorption 0.15–0.58% (measured by urinary recovery over 7 days at 17 g/day) | Lack of systemic exposure accounts for the excellent safety profile and minimal drug interaction potential; acts entirely within the GI lumen |
| Distribution | Not applicable; confined to the GI lumen. Trace amounts absorbed are not protein-bound | No systemic distribution; no concerns about tissue accumulation or organ toxicity at recommended doses |
| Metabolism | Not metabolised; chemically inert polymer. Not fermented by colonic bacteria (no hydrogen or methane production) | No hepatic processing; no risk of drug-metabolite interactions; less gas production than fermentable osmotic laxatives (e.g., lactulose) |
| Elimination | ~93% recovered in stool within 24 h; trace amounts (<0.6%) excreted in urine by kidneys | No dose adjustment for hepatic impairment; use with caution in renal disease due to theoretical electrolyte concerns with high-volume use |
Side Effects
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| GI symptoms (overall) | 32% (vs 25% placebo) | Predominantly diarrhea, loose stools, flatulence, and nausea; most GI adverse events attenuate markedly after the first week of use (DiPalma 2007) |
| Diarrhea | 11% | Dose-related; more common at 34 g/day and in elderly nursing home patients; discontinue if persistent |
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Flatulence | 7% | Less than with lactulose since PEG is not fermented by colonic bacteria |
| Nausea | 6% | Usually mild and transient; may improve if taken with food |
| Abdominal pain / cramping | 5% | Related to increased stool volume and colonic distension; dose-dependent |
| Loose stools | 4% | Expected pharmacological effect at the threshold between efficacy and excess; reduce dose if bothersome |
| Abdominal distension / bloating | 3% | Less common than with fermentable osmotic laxatives |
| Adverse Effect | Estimated Frequency | Typical Onset | Required Action |
|---|---|---|---|
| Dehydration / electrolyte imbalance | Rare at 17 g/day; increased with high-dose or bowel prep use | Days | Ensure adequate fluid intake; check electrolytes if symptomatic (confusion, dizziness, seizures); correct imbalance |
| Allergic / hypersensitivity reactions (urticaria, anaphylaxis) | Very rare (postmarketing) | Minutes to hours | Discontinue PEG; treat anaphylaxis per protocol; permanent avoidance of PEG-containing products |
| Ischaemic colitis / mucosal ulceration (bowel prep setting) | Very rare; risk increased with concurrent stimulant laxatives | During bowel prep | Stop preparation; evaluate with imaging and colonoscopy; surgical consultation if needed |
In the 7-day RCT by McGraw (2016, N=203), no deaths, serious adverse events, or discontinuations due to adverse events were reported in the PEG 3350 group. In the 24-week DiPalma study, GI adverse events in the PEG group decreased from 34% in weeks 1–12 to 9% in weeks 13–24, indicating tolerance improves with continued use. Discontinuation for adverse effects is uncommon and typically driven by persistent diarrhea or bloating.
PEG 3350 is chemically inert, not absorbed, not metabolised, and not fermented. No new adverse events emerged with prolonged exposure in the 6-month chronic constipation safety study. No clinically significant effects on laboratory values (including electrolytes) have been demonstrated at the standard 17 g dose. This safety profile distinguishes PEG 3350 from stimulant laxatives which carry risks of electrolyte depletion and dependence with chronic use.
Drug Interactions
PEG 3350 has an exceptionally low drug interaction potential because it is not absorbed from the GI tract, not metabolised, and does not affect active glucose or electrolyte transport. The FDA prescribing information states that no specific drug interactions have been demonstrated. However, clinically relevant interactions may arise indirectly through altered GI transit time or fluid/electrolyte effects, particularly at high doses used for bowel preparation.
Monitoring
-
Stool Frequency & Consistency
Daily during treatment
Routine Treatment goal is soft, formed stools without straining. If no bowel movement after 7 days (OTC) or 2 weeks (Rx), discontinue and reassess. If excessive diarrhea develops, stop PEG and re-evaluate. -
Hydration Status
Ongoing
Routine Particularly important in elderly patients, children, and patients using high-dose PEG for bowel preparation or disimpaction. Dehydration from diarrhea can cause confusion and seizures. -
Electrolytes
If prolonged use or bowel prep
Trigger-based Not routinely needed at 17 g/day (no clinically significant electrolyte changes demonstrated). Check electrolytes if patient develops significant diarrhea, is on diuretics, or is using high-dose PEG for bowel preparation. -
Bowel Obstruction Symptoms
Before initiation
Routine Evaluate for nausea, vomiting, abdominal pain, and distension before starting PEG. These symptoms may indicate bowel obstruction, which is a contraindication to use.
Contraindications & Cautions
Absolute Contraindications
- Known or suspected bowel obstruction — PEG increases intraluminal volume and could worsen obstruction or cause perforation
- Known hypersensitivity to polyethylene glycol — urticaria and anaphylaxis have been reported postmarketing
Relative Contraindications (Specialist Input Recommended)
- Symptoms suggestive of appendicitis or inflamed bowel — evaluate before initiating PEG (nausea, vomiting, abdominal pain, distension)
- Renal impairment — OTC label advises against use without medical supervision; risk of electrolyte imbalance with excessive use
Use with Caution
- Elderly patients (especially nursing home residents) — higher incidence of diarrhea at the standard 17 g dose; may need dose reduction
- Patients requiring thickened liquids — PEG interacts with starch-based thickeners, reducing viscosity; use xanthan gum-based alternatives
- Inflammatory bowel disease (active flare) — increased GI motility may worsen symptoms; use only under gastroenterology guidance
- Pregnancy — minimal absorption suggests low risk, but no adequate human studies; use if benefit outweighs risk
The OTC label advises patients to consult a healthcare provider before use if they have nausea, vomiting, or abdominal pain; irritable bowel syndrome; a sudden change in bowel habits lasting more than 2 weeks; or renal disease. Patients should stop use and consult a provider if they experience rectal bleeding, diarrhea that worsens, or need to use PEG for more than 7 days. These warnings ensure appropriate evaluation for underlying pathology before attributing symptoms to simple constipation.
Patient Counselling
Purpose of Therapy
Polyethylene glycol 3350 is a gentle, osmotic laxative that helps relieve constipation by drawing water into the stool, making it softer and easier to pass. It does not stimulate the bowel directly and will not cause cramping in most patients. It is tasteless and odourless when dissolved.
How to Take
Measure one dose (17 g) using the measuring cap provided with the bottle, or use one single-dose packet. Stir the powder into 4 to 8 ounces (120–240 mL) of any beverage (water, juice, coffee, tea, or soda) until completely dissolved. Drink the mixture right away. Do not drink it if there are any undissolved lumps. Do not add starch-based thickeners. Take once daily, preferably in the morning. Allow 1 to 3 days for a bowel movement to occur. Do not use for more than 7 days without consulting a healthcare provider.
Sources
- Polyethylene Glycol 3350 NF — FDA-approved prescribing information. DailyMed Primary regulatory source for Rx PEG 3350: dosing, mechanism, contraindications, and the statement that no tachyphylaxis or drug interactions have been demonstrated.
- MiraLAX (polyethylene glycol 3350) OTC product labelling. Bayer HealthCare. DailyMed OTC label with consumer dosing (17 g once daily for up to 7 days), preparation instructions, and self-medication warnings.
- DiPalma JA, Cleveland MV, McGowan J, Herrera JL. A randomized, multicenter, placebo-controlled trial of polyethylene glycol laxative for chronic treatment of chronic constipation. Am J Gastroenterol. 2007;102(7):1436–1441. DOI 24-week RCT (N=304) establishing long-term efficacy and safety of PEG 3350 17 g/day for chronic constipation; source of GI adverse event rates (32% vs 25% placebo).
- DiPalma JA, DeRidder PH, Orlando RC, et al. A randomized, placebo-controlled, multicenter study of the safety and efficacy of a new polyethylene glycol laxative. Am J Gastroenterol. 2000;95(2):446–450. DOI Pivotal 14-day RCT demonstrating superiority of PEG 3350 17 g/day over placebo for increasing bowel movement frequency and stool weight.
- McGraw T. Polyethylene glycol 3350 in occasional constipation: a one-week, randomized, placebo-controlled, double-blind trial. World J Gastrointest Pharmacol Ther. 2016;7(2):274–282. DOI 7-day RCT (N=203) confirming PEG 3350 efficacy for occasional constipation with significant relief of straining and hard stools; no serious AEs or discontinuations.
- Chang L, Chey WD, Imdad A, et al. AGA Clinical Practice Guideline on the Pharmacological Management of Chronic Idiopathic Constipation. Gastroenterology. 2023;164(7):1086–1106. DOI AGA guideline recommending PEG as a first-line osmotic laxative for chronic idiopathic constipation based on high-quality evidence.
- Tabbers MM, DiLorenzo C, Berger MY, et al. Evaluation and treatment of functional constipation in infants and children: evidence-based recommendations from ESPGHAN and NASPGHAN. J Pediatr Gastroenterol Nutr. 2014;58(2):258–274. DOI Joint ESPGHAN/NASPGHAN guideline recommending PEG as first-line treatment for pediatric functional constipation with weight-based dosing.
- Schiller LR. Review article: the therapy of constipation. Aliment Pharmacol Ther. 2001;15(6):749–763. DOI Comprehensive review of constipation pharmacotherapy including the osmotic mechanism and non-fermentable properties of PEG.
- Hammer HF, Santa Ana CA, Schiller LR, Fordtran JS. Studies of osmotic diarrhea induced in normal subjects by ingestion of polyethylene glycol and lactulose. J Clin Invest. 1989;84(4):1056–1062. DOI Foundational physiology study demonstrating PEG’s osmotic water retention mechanism and confirming absence of colonic fermentation.
- Corazziari E, Badiali D, Bazzocchi G, et al. Long term efficacy, safety, and tolerability of low daily doses of isosmotic polyethylene glycol electrolyte balanced solution (PMF-100) in the treatment of functional chronic constipation. Gut. 2000;46(4):522–526. DOI 6-month safety study demonstrating sustained efficacy with progressively decreasing dosage and 77% complete symptom resolution.
- Dupont C, Leluyer B, Maamri N, et al. Double-blind randomized evaluation of clinical and biological tolerance of polyethylene glycol 4000 versus lactulose in constipated children. J Pediatr Gastroenterol Nutr. 2005;41(5):625–633. DOI Comparative pediatric trial showing PEG efficacy comparable to lactulose with fewer side effects (less vomiting, less flatulence).
- Adamcewicz M, Bearelly D, Porat G, Friedenberg FK. Mechanism of action and toxicities of purgatives used for colonoscopy preparation. Expert Opin Drug Metab Toxicol. 2011;7(1):89–101. DOI Reviews PEG pharmacology in bowel preparation context, including low systemic absorption (0.15–0.58%) and electrolyte safety considerations.