Does Miralax (polyethylene glycol 3350) contain magnesium?

Does Miralax Contain Magnesium?

No, Miralax (polyethylene glycol 3350) does not contain magnesium. Miralax is composed solely of polyethylene glycol 3350, which is a synthetic polyglycol with an average molecular weight of 3350 1.

Composition of Miralax

• Miralax consists of polyethylene glycol 3350 (PEG 3350), which is a white powder that is freely soluble in water 1
• According to the FDA drug label, Miralax is described as "a synthetic polyglycol having an average molecular weight of 3350" with the chemical formula HO(C2H4O)nH 1
• Unlike some other laxative preparations, Miralax does not contain electrolytes such as magnesium, sodium, or potassium 2

Mechanism of Action

• Miralax (PEG 3350) works as an osmotic laxative by sequestering fluid in the bowel 2
• It is considered iso-osmotic but not isotonic, which is why it is often recommended to mix it with a sports drink when used for bowel preparation 2
• PEG 3350 is a poorly absorbed polymer that works through osmotic action to increase water content in the stool 2

Comparison with Magnesium-Containing Laxatives

• Some other laxative formulations do contain magnesium, such as:

  • Magnesium hydroxide (Milk of Magnesia) 3, 4
  • Magnesium citrate (often used in combination with sodium picosulfate) 2
  • Magnesium sulfate (included in some bowel preparation formulations) 2

• Magnesium-containing laxatives work through a different mechanism than PEG 3350:

  • They are osmotic agents that draw water into the intestinal lumen 2
  • They can lead to hypermagnesemia, especially in patients with renal impairment 2

Clinical Implications

• The absence of magnesium in Miralax makes it suitable for patients who need to avoid magnesium, such as those with renal impairment 2
• When prescribing laxatives, it's important to note that magnesium and sulfate salts can lead to hypermagnesemia and should be used cautiously in renal impairment 2
• Miralax is often used off-label as a bowel preparation regimen, though it is not FDA-approved for this purpose 2

Safety Considerations

• Miralax does not cause electrolyte imbalances related to magnesium 5
• Unlike magnesium-containing laxatives, Miralax does not carry contraindications related to hypermagnesemia or congestive heart failure 2
• Studies comparing PEG 3350 with magnesium-containing laxatives have found both to be effective for treating constipation, with PEG 3350 often having better acceptability in patients over 4 years of age 4

In summary, Miralax contains only polyethylene glycol 3350 and does not contain magnesium or other electrolytes, making it distinct from magnesium-based laxatives such as magnesium hydroxide, magnesium citrate, or magnesium sulfate.