Miralax MOA (Mechanism of Action of Polyethylene Glycol)

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Miralax is the brand name of Polyethylene Glycol. It is a commonly used drug used to relieve constipation and for bowel preparation before a colonoscopic procedure. Miralax MOA as to how it acts to relieve constipation is discussed here.

What is Miralax?

Miralax or polyethylene Glycol 3350 is an osmotic laxative. It is available in the form of capsules, sachets, and syrups. Miralax can be used by both children and adults for the relief of constipation and before preparing the bowel for a procedure.

How does Miralax relieve constipation (MOA)?

Miralax is an osmotic laxative. It relieves constipation by increasing the water content of the stools. Osmotically active substances retain water by indrawing water from the gastrointestinal mucosa.

Miralax (Polyethylene Glycol or PEG) contains multiple monomers of ethylene glycol that are catalyzed in the gastrointestinal tract. It is not absorbed into the systemic circulation as it forms hydrogen bonds with water molecules. 

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This results in water retention in the gastrointestinal tract, softens stools consistency, and increases the transit of stools from the intestines.

Miralax contains PEG (Polyethylene Glycol) that has a better taste and is one of the preferred drugs for the treatment of chronic constipation because of the minimal adverse effects.

Miralax or PEG electrolyte lavage solution is relatively less safe compared to PEG laxative.

How should you use Miralax?

Miralax or PEG is used for the treatment of chronic constipation. When used as an OTC medicine, the duration of treatment should not exceed 14 days.

Adults should take 17 gms of the drug mixed with a glass of water or 8 ounces of water and take it once daily. It may take 2 to 4 days for the first bowel movements to occur.

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When used to cleanse bowels before colonoscopy, 238 gms of Miralax is mixed with 2 liters of sports drink. The patient is asked to drink the solution one day before surgery.

If the procedure is in the afternoon, one liter may be taken one day before and one liter in the morning on the day of the procedure.

In children, the dose is administered based on the child’s weight. For the treatment of chronic constipation, it is given in a dose of 0.2 to 0.8 gms/kg/day up to a maximum dose of 17 gms per day.

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Miralax is category C in Pregnancy. This means data is limited. However, it can be used for the treatment of constipation by lactating mothers. It does not enter the milk of the nursing mother as it is not absorbed.

Contraindications and Side effects:

If bowel obstruction is suspected, it should be avoided. Similarly, it should be avoided in patients with acute appendicitis, inflammatory bowel diseases, and in patients who are allergic to the drug.

Miralax may reduce the levels of digoxin in the blood because of impaired absorption. It should also be avoided in advanced kidney disease.

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Other Names of Miralax:

Miralax is also available by other brand names. These include Glycolax, Gavilax, Healthylax, and Pegylax.