Can Miralax Cause Colitis?
No, there is no evidence that Miralax (polyethylene glycol 3350) causes colitis. The FDA-approved drug label for polyethylene glycol does not list colitis as a side effect, and there are no clinical guidelines or research studies that establish a causal link between Miralax and colitis 1.
Understanding Miralax (Polyethylene Glycol 3350)
Miralax is an osmotic laxative that works by:
- Drawing water into the colon to soften stool and increase bowel movements
- Being poorly absorbed in the intestinal tract
- Working through an osmotic mechanism rather than through irritation of the intestinal lining
Common Side Effects
According to the FDA drug label, the most common side effects of Miralax include:
- Loose, watery, more frequent stools 1
- Bloating
- Abdominal discomfort
- Nausea
Safety Profile
Miralax has been extensively studied and has demonstrated a favorable safety profile:
- Clinical studies have shown it to be safe and effective for the treatment of constipation 2
- It does not cause significant electrolyte abnormalities even when used in higher doses 3
- It has been safely used in both adults and children 4
Colitis: Causes and Risk Factors
Colitis (inflammation of the colon) is typically caused by:
- Inflammatory bowel diseases like ulcerative colitis
- Infections (bacterial, viral, or parasitic)
- Ischemia (reduced blood flow to the colon)
- Medications (NSAIDs, antibiotics)
- Radiation therapy
Medications Known to Cause Colitis
Several medications have been associated with colitis, but polyethylene glycol is not among them:
- Bisacodyl has been associated with rare occurrences of ischemic colitis 5
- Alosetron (a 5-HT3 receptor antagonist used for IBS-D) was temporarily withdrawn from the market due to reports of ischemic colitis 5
- Docetaxel-containing regimens have been reported to cause ischemic colitis in rare cases 5
Clinical Considerations When Using Miralax
When to Use Caution
The FDA label recommends asking a doctor before using Miralax if you have:
- Nausea, vomiting, or abdominal pain
- A sudden change in bowel habits lasting over 2 weeks
- Irritable bowel syndrome 1
Appropriate Use
- Miralax is commonly used as a bowel preparation for colonoscopy, often in combination with other agents 5, 6, 7
- It's also used for the treatment of constipation at lower doses (17-34g daily) 2
- For bowel preparation, split-dosing regimens have shown better efficacy than single-dose regimens 3
Bowel Preparation Considerations
When using Miralax for bowel preparation:
- Split-dose regimens are more effective than single-dose regimens 3
- Traditional PEG with electrolytes (GoLytely) has shown superior bowel cleansing compared to Miralax/Gatorade combinations, though patients prefer the taste of Miralax 6, 7
- Miralax has not been shown to cause significant electrolyte disturbances even when used in higher doses for bowel preparation 3
Bottom Line
Miralax is a safe osmotic laxative that works by drawing water into the colon. It has not been associated with causing colitis in clinical studies or post-marketing surveillance. If a patient develops symptoms of colitis while taking Miralax, other causes should be investigated, as the association is likely coincidental rather than causal.