MiraLAX Dosing for Colonoscopy Bowel Preparation
For colonoscopy bowel preparation, the standard off-label regimen uses 238 grams of MiraLAX (polyethylene glycol 3350) mixed with 64 ounces of a sports drink, typically administered as a split-dose regimen, though this approach is inferior to FDA-approved colonoscopy preparations and is not FDA-approved for this indication. 1, 2
Critical Context: FDA Approval Status
- MiraLAX (PEG-3350) is NOT FDA-approved for colonoscopy preparation and should be considered inferior to FDA-approved regimens 1, 2
- The FDA approval for MiraLAX is limited to constipation treatment at 17 grams daily for up to 7 days 3
- Despite lack of FDA approval, this regimen remains widely used in community practice due to perceived better tolerability 2, 4
Standard Off-Label Colonoscopy Preparation Regimen
Total dose: 238 grams of PEG-3350 powder (equivalent to fourteen 17-gram packets) mixed with 64 ounces of Gatorade or similar sports drink 2, 5, 4
Split-Dose Administration (Preferred)
- Split-dosing is significantly more effective than single-dose administration 4
- Administer approximately half (119 grams) the evening before colonoscopy 2, 4
- Administer the remaining half (119 grams) on the morning of the procedure 2, 4
- Complete the last dose at least 2 hours before procedure time 1
Adjunctive Bisacodyl
- Many protocols add bisacodyl 5-10 mg tablets as an adjunct to improve efficacy 2, 5
- However, bisacodyl carries a rare risk of ischemic colitis 1
Critical Safety Requirement: Sports Drink Mixing
PEG-3350 MUST be mixed with a sports drink (not plain water) because it is iso-osmotic but NOT isotonic 1, 2
- Plain water mixing poses risk of hyponatremia, particularly with evening-before dosing 2
- Sports drinks provide necessary electrolytes that PEG-3350 powder lacks 1, 2
- Ensure powder is fully dissolved before drinking 3
Efficacy Evidence: Inferior to FDA-Approved Preparations
Multiple high-quality studies demonstrate that MiraLAX/Gatorade produces inferior bowel cleansing compared to FDA-approved preparations:
- Split-dose MiraLAX/Gatorade (238g) was less effective than 4L split-dose GoLytely, with Ottawa scores of 4.8 vs 4.12 (lower is better) 4
- Single-dose PEG-3350+Gatorade+bisacodyl resulted in significantly inferior bowel preparation compared to split-dose 2L PEG-ascorbic acid, with lower Boston Bowel Preparation Scale scores in all colon segments 6
- MiraLAX alone or combined with bisacodyl or lubiprostone was less effective than GoLytely (Ottawa scores 6.3-6.9 vs 5.1) 5
Recommended Alternative: FDA-Approved Preparations
The US Multi-Society Task Force on Colorectal Cancer (2025) recommends FDA-approved preparations over off-label MiraLAX 1, 2:
- 2-liter PEG-ELS with ascorbate (split-dose) - isotonic, FDA-approved 1, 2
- 1-liter PEG-ELS with ascorbate (split-dose) - ultra-low volume, FDA-approved 1, 2
- Both provide superior efficacy with adequate safety profiles 1
Patient Tolerability Considerations
- MiraLAX/Gatorade regimens are rated as more satisfactory by patients than high-volume preparations 5, 4
- 96.8% of MiraLAX/Gatorade patients willing to repeat vs 75% for GoLytely 4
- However, patient preference should not override the superior efficacy of FDA-approved preparations for adequate bowel visualization 2, 6
Common Pitfalls to Avoid
- Do not use plain water - must use sports drink for electrolyte balance 1, 2
- Do not use single-dose regimens - split-dosing is significantly more effective 4
- Do not assume equivalent efficacy to FDA-approved preparations - evidence clearly shows inferiority 5, 6
- Verify no contraindications including bowel obstruction, ileus, or allergy to ingredients 1
Clinical Bottom Line
If prescribing off-label MiraLAX for colonoscopy preparation despite its inferior efficacy, use 238 grams (fourteen 17-gram packets) mixed with 64 ounces of sports drink as a split-dose regimen, but strongly consider switching to FDA-approved 2L or 1L PEG-ELS with ascorbate preparations for superior bowel cleansing quality. 1, 2, 6