MiraLAX
MiraLAX
Generic Name
MiraLAX
Mechanism
- MiraLAX contains polyethylene glycol 3350 (PEG‑3350), an osmotic laxative that is inert in the gastrointestinal tract.
- PEG‑3350 draws water into the colon by osmosis, increasing stool volume and intestinal transit time.
- The drug is not absorbed; it acts locally, producing a gentle, sustained laxative effect with minimal systemic side effects.
Pharmacokinetics
| Parameter | Details |
| Absorption | None – remains in the GI lumen. |
| Distribution | Local luminal activity; negligible systemic distribution. |
| Metabolism | Not metabolized. |
| Excretion | Eliminated unchanged with stool. |
| Onset of Action | 1‑3 days after initiation. |
| Toxicity | Rare; mainly associated with over‑use leading to volume overload and electrolyte derangements. |
Indications
- Chronic constipation in adults and children (≥1 year).
- Prevention of constipation during drug therapy (e.g., opioids, corticosteroids).
- Relief of mild to moderate constipation in pregnancy.
- Indications for short‑term use in irritable bowel syndrome‑constipation (IBS‑C) when other therapies fail.
Contraindications
- Contraindications:
- Mechanical bowel obstruction, ileus, or toxic megacolon.
- Known hypersensitivity to PEG 3350 or any excipients.
- Warnings:
- Use cautiously in patients with renal or hepatic insufficiency – monitor hydration and electrolytes.
- Potential for drug displacement; may alter absorption of other oral medications.
- Adequate fluid intake is essential; may cause dehydration if fluids are inadequate.
- In rare cases, can precipitate electrolyte disturbances (hyponatremia, hypokalemia).
Dosing
| Population | Dose | Administration |
| Adults & Adolescents (≥18 y) | 17 g (≈5 tsp) powder + 4 fl oz water | Once daily (or split into two doses) |
| Children (1 – 12 y) | 0.5 g/kg/day (max 17 g) | Once or twice daily with adequate fluid |
| Older Adults | Same as adults; monitor renal function | |
| Pregnancy/Breastfeeding | Same as adults | Safe with adequate hydration |
• Mixing: Stir with water, juice, or milk; avoid hot liquids as they can increase irritation.
• Timing: Can be taken at any time of day; split dosing may improve tolerability.
Adverse Effects
- Common:
- Bloating, abdominal cramping, flatulence.
- Mild nausea, diarrhea (if overdosed).
- Oral irritation if syrup form used excessively.
- Serious:
- Electrolyte imbalance (e.g., hyponatremia, hypokalemia) with misuse.
- Volume overload in heart failure or renal impairment.
- Rectal irritation leading to bleeding (rare).
- Intestinal obstruction in susceptible patients.
Monitoring
- Hydration status: Assess intake and urinary output; encourage ≥2 L fluids/day.
- Electrolytes (Na⁺, K⁺, Cl⁻) if prolonged use or underlying disease.
- Bowel pattern: Frequency, stool consistency, and straining episodes.
- Weight: Monitor for fluid shifts in patients with cardiovascular/renal disease.
- Renal function (creatinine, BUN) in chronic use cases.
Clinical Pearls
- Tolerability: Splitting the dose (e.g., 8 g in the morning + 9 g in the evening) reduces bloating and cramping in sensitive patients.
- Pregnancy & Lactation: PEG‑3350 is G‑category A; it’s one of the safest OTC laxatives for pregnant patients, especially those taking iron supplements that cause constipation.
- Drug Interactions: As PEG is not absorbed, it can reduce the efficacy of concurrent oral drugs by accelerating transit; give non‑extended‑release medications 2 h before/after PEG if necessary.
- Use in IBS‑C: Short‑term treatment (≤3 months) can effectively lower stool frequency; long‑term use may increase side‑effect burden.
- Storage: Keep at room temperature, away from heat and moisture; powdered form is stable for 1 year unopened.
- Emergency: In severe constipation with signs of obstruction, discontinue PEG‑3350 immediately and evaluate for colonic pathology.
> *Reference: Mayo Clinic, UpToDate, FDA prescribing information – all consistently document PEG‑3350’s safety profile, dosing, and indications as outlined above.*