Can you take Miralax (polyethylene glycol) with Metamucil (psyllium)?

Taking Miralax with Metamucil for Constipation

Yes, you can take Miralax (polyethylene glycol) with Metamucil (psyllium), but it's generally better to separate their administration by at least 2 hours to prevent potential interference with absorption and effectiveness.

Mechanism of Action

• Miralax (polyethylene glycol/PEG): Works as an osmotic laxative that draws water into the intestinal lumen, softening stool and increasing bowel movement frequency. It is not absorbed systemically and works locally in the colon 1.

• Metamucil (psyllium): Functions as a bulk-forming laxative that absorbs water to form a gel-like mass, increasing stool bulk and stimulating bowel movements 1.

Effectiveness and Clinical Use

The American Gastroenterological Association recommends polyethylene glycol (PEG) as the first-line pharmacological treatment for chronic constipation, with a strong recommendation and moderate certainty of evidence 1. PEG can increase complete spontaneous bowel movements by approximately 2.9 per week.

Psyllium (Metamucil) is considered a soluble fiber that improves stool viscosity and transit time in addition to increasing bulk 2. It's generally safe during pregnancy due to its lack of systemic absorption 2.

Important Considerations When Using Together

1. Timing: Separate administration by at least 2 hours to prevent Metamucil from interfering with Miralax's action or absorption of other medications.

2. Hydration: Both medications require adequate fluid intake to work properly and prevent complications:

   • Metamucil needs sufficient water to form its gel-like consistency
   • Miralax requires water for its osmotic effect

3. Specific Situations:

   • For opioid-induced constipation, fiber supplements like Metamucil are unlikely to be effective on their own 1
   • For pelvic floor dyssynergia, combining laxatives with biofeedback did not offer significant therapeutic benefit over biofeedback alone 3

4. Potential Concerns: Excessive fiber and osmotic laxatives like lactulose can cause maternal bloating during pregnancy 2, and similar effects might occur with the combination of Metamucil and Miralax.

Contraindications

• Do not use either medication if you have:
  • Bowel obstruction
  • Ileus
  • Allergy/hypersensitivity to ingredients 2

Dosing Guidelines

• Miralax: 17-34g daily 1
• Metamucil (psyllium): Typically 1 rounded teaspoon 1-3 times daily with 8 oz of water

Special Considerations

A 2004 study found that taking psyllium for four days before colonoscopy with polyethylene glycol preparation actually worsened the efficacy of bowel preparation 4. This suggests that these agents may interact in ways that reduce effectiveness when used simultaneously for certain purposes.

However, a 2013 review suggested that the combination of psyllium and PEG could potentially combine the advantages of fiber and isotonic solutions and represent an important therapeutic option for patients suffering from chronic constipation 5.

For most patients with routine constipation, either agent alone may be sufficient, with PEG being the first-line recommendation for chronic constipation according to guidelines 1.