Miralax Dosing
The standard adult dose of Miralax (polyethylene glycol 3350) is 17 grams once daily, mixed in 8 ounces of liquid 1.
Adult Dosing
- Standard dose: 17 grams (one capful) once daily, dissolved in 8 ounces of any beverage 1
- Timing: Can be taken at any time of day
- Duration: FDA-approved for short-term use (occasional constipation), though clinical trials demonstrate efficacy and safety for up to 6 months in chronic idiopathic constipation 1
- Dose adjustment: While no clear maximum dose exists, the dose can be titrated based on symptom response and side effects 1
Alternative Dosing Regimens
Some studies used 17.5 grams twice daily (PEG with electrolytes) dissolved in 250 mL of water, though this is not the standard FDA-approved regimen 1. The once-daily 17-gram dose remains the recommended starting point.
For rapid relief of acute constipation, higher single doses have been studied (68 grams in 500 mL of flavored water provided relief within 24 hours), but this is not standard practice 2.
Pediatric Dosing
For children, the effective maintenance dose averages 0.8-0.84 g/kg/day 3, 4:
- Typical range: 0.27 to 1.42 g/kg/day, adjusted every 3 days to achieve 2 soft stools per day 3
- Children under 24 months: Limited evidence exists, with reported doses ranging from 0.45 to 1.1 g/kg/day for PEG 3350 4
- Fecal impaction treatment: Higher doses of 1-1.5 g/kg/day for 3 days are effective for disimpaction 5
Practical Measurement for Pediatric Doses
Since precise gram measurements can be challenging at home:
- 1 leveled teaspoon ≈ 3.3 grams
- 1 leveled tablespoon ≈ 10 grams
- 1 capful = 17 grams 6
Using a dedicated measuring device and leveling the dose improves consistency 6.
Important Clinical Considerations
Common side effects include abdominal distension, loose stools, flatulence, nausea, bloating, and diarrhea 1. These are typically mild to moderate and dose-related.
Fluid intake: The medication should always be mixed with adequate fluid (8 ounces minimum for adults) 1. This is critical for both efficacy and safety.
Response timeline: Patients typically see best efficacy by week 2 of treatment, with sustained improvement over 6 months 1. For acute relief, effects may begin within 14-24 hours at standard dosing 2.
No electrolyte disturbances: PEG 3350 without electrolytes does not cause clinically significant changes in serum electrolytes, even with long-term use 2, 5, 7.
Treatment algorithm: The 2023 AGA-ACG guidelines recommend PEG as first-line pharmacological therapy for chronic idiopathic constipation, either after a trial of fiber supplementation for mild constipation or in combination with fiber 1. This reflects its strong evidence base (moderate certainty), favorable safety profile, low cost, and over-the-counter availability.