Miralax (Polyethylene Glycol) Dosing for Constipation
The recommended initial dose of Miralax (polyethylene glycol 3350) for treating constipation is 17g once daily, dissolved in 4-8 ounces (120-240 ml) of liquid, with dose adjustments based on symptomatic response. 1
Standard Dosing Recommendations
- Initial dose: 17g (one capful/packet) once daily
- Administration: Dissolve in 4-8 ounces of any beverage
- Duration: Can be safely used for up to 12 months with no evidence of tachyphylaxis 2
- Dose adjustment: Based on individual response, with no established maximum dose 1
Efficacy Timeline
- Most patients experience relief within the first week of treatment
- Full efficacy is typically observed by the second week of treatment 3
- Treatment success rate is approximately 78.3% compared to 39.1% with placebo 4
Special Dosing Situations
For Severe Constipation or Fecal Impaction
- Higher doses (up to 8 packets of 13.8g in 4-6 hours) may be considered
- Requires close monitoring of response and side effects 1
For Rapid Relief (24-hour response)
- A 68g dose has been shown to provide effective relief within 24 hours
- This higher dose resulted in an average of 2.2 bowel movements in 24 hours versus 0.5 with placebo 5
- Time to first bowel movement averaged 14.8 hours with the 68g dose 5
Treatment Algorithm
First-line approach:
- Start with 17g PEG daily
- Ensure adequate hydration (essential during treatment)
- Encourage increased fluid intake and exercise
If inadequate response after 2-3 days:
- Consider increasing dose (no established maximum)
- Monitor for side effects
For severe constipation requiring rapid relief:
- Consider higher dose (68g) for faster action 5
Safety Considerations
- Common side effects: abdominal distension, flatulence, nausea, and abdominal discomfort 1
- No significant changes in electrolytes, calcium, glucose, BUN, creatinine, or serum osmolality have been observed, even at higher doses 5
- Safe for elderly patients with similar efficacy and side effect profiles 4, 2
- No evidence of tachyphylaxis with long-term use 2
Important Clinical Pearls
- Constipation often returns after discontinuation, with 61.7% of patients requiring additional treatment within 30 days after stopping PEG 1
- PEG is effective for constipation caused by medications, with 78.3% treatment success compared to 39.1% with placebo 4
- Monthly cost ranges from $10-$45 1
- Adequate hydration is essential during treatment to minimize side effects 1
Monitoring
- Track frequency and consistency of bowel movements
- Assess relief of constipation symptoms
- Monitor for side effects, particularly gastrointestinal complaints