MiraLAX - Drug Monograph

Introduction

MiraLAX (polyethylene glycol 3350) is an over-the-counter osmotic laxative used for the treatment of occasional constipation. It is one of the most commonly recommended laxatives by healthcare providers due to its favorable safety profile and efficacy. Unlike stimulant laxatives, MiraLAX works by drawing water into the colon to soften stool and promote bowel movements without causing harsh cramping or dependency.

Mechanism of Action

MiraLAX exerts its therapeutic effect through osmotic activity. Polyethylene glycol 3350 is a non-absorbable polymer that works by hydrogen bonding with water molecules in the intestinal lumen. This creates an osmotic gradient that draws water into the colon, resulting in stool softening, increased stool volume, and enhanced peristalsis. The medication does not undergo metabolism or systemic absorption, acting locally within the gastrointestinal tract.

Indications

• Treatment of occasional constipation
• Bowel preparation prior to colonoscopy (often used off-label in combination with other agents)
• Maintenance of regularity in patients with chronic constipation (under medical supervision)

Dosage and Administration

• 17 grams (1 heaping tablespoon) dissolved in 4-8 ounces of water, juice, soda, coffee, or tea
• Administer once daily
• Onset of action typically occurs within 24-72 hours

• Safety and effectiveness in children under 17 years have not been established
• However, many pediatric gastroenterologists use it off-label with dosing based on weight (0.5-1.5 g/kg/day)

• Geriatric patients: No dosage adjustment required
• Renal impairment: No specific recommendations (minimal systemic absorption)
• Hepatic impairment: No dosage adjustment necessary

Pharmacokinetics

Contraindications

• Known hypersensitivity to polyethylene glycol or any component of the formulation
• Bowel obstruction or ileus
• Toxic megacolon
• Acute abdominal pain of unknown origin
• Inflammatory bowel disease (unless specifically recommended by a gastroenterologist)

Warnings and Precautions

• Use with caution in patients with impaired gag reflex, reflux, or swallowing difficulties due to aspiration risk
• Prolonged use (beyond one week) without medical supervision should be avoided
• Patients with renal impairment should use with caution (though minimal absorption occurs)
• May cause electrolyte imbalances with prolonged use, though less likely than with stimulant laxatives
• Discontinue use if severe diarrhea, abdominal pain, or rectal bleeding occurs

Drug Interactions

• Although systemic absorption is minimal, theoretical interactions exist with oral medications due to potential altered gastrointestinal transit time
• May reduce absorption of other orally administered drugs (separate administration by at least 2 hours)
• No known clinically significant pharmacokinetic drug interactions
• Caution with other laxatives or medications that affect gastrointestinal motility

Adverse Effects

• Abdominal bloating
• Flatulence
• Abdominal cramping
• Nausea
• Diarrhea (especially with higher doses)

• Allergic reactions (rash, pruritus, urticaria)
• Electrolyte imbalances (with prolonged use)
• Dehydration (if inadequate fluid intake)

• Severe allergic reactions (anaphylaxis)
• Aspiration pneumonia (if improperly administered)
• Severe electrolyte disturbances

Monitoring Parameters

• Bowel movement frequency and consistency
• Hydration status (especially in elderly or debilitated patients)
• Electrolytes with prolonged use (>3 months)
• Abdominal examination if symptoms persist or worsen
• Patient weight in cases of chronic use
• Signs of allergic reactions

Patient Education

• Dissolve powder completely in 4-8 ounces of liquid before ingestion
• Maintain adequate fluid intake throughout treatment
• Expected onset of action is 1-3 days
• Do not use for more than 7 days without consulting a healthcare provider
• Report severe abdominal pain, rectal bleeding, or no bowel movement after use
• Store at room temperature away from moisture
• Keep out of reach of children
• Not for use in children under 17 years unless directed by a physician
• May be taken with or without food

References

1. FDA Label: MiraLAX (polyethylene glycol 3350) OTC Monograph. Accessed January 2023. 2. American Gastroenterological Association Technical Review on Constipation. Gastroenterology. 2013;144(1):218-238. 3. Brenner DM, Shah M. Chronic Constipation. Gastroenterol Clin North Am. 2016;45(2):205-216. 4. Lee-Robichaud H, Thomas K, Morgan J, Nelson RL. Lactulose versus Polyethylene Glycol for Chronic Constipation. Cochrane Database Syst Rev. 2010;(7):CD007570. 5. 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. 6. Piesman M, Fukudo S, Emmanuel A, et al. Evidence-Based Dietary Management of Functional Gastrointestinal Symptoms: The FODMAP Approach. J Gastroenterol Hepatol. 2010;25(2):252-258.