What is the recommended dose of Miralax (polyethylene glycol 3350) for adults and for children?

Recommended Miralax Dose

For adults with chronic constipation, the recommended dose of Miralax (polyethylene glycol 3350) is 17 grams once daily, mixed in 8 ounces of liquid. 1

Adult Dosing

The FDA-approved dose is 17 grams daily for occasional constipation, though clinical trials have demonstrated efficacy and safety for chronic idiopathic constipation for up to 6 months at this dose 1. This represents the standard capful that comes with the bottle 2.

Dosing Variations in Clinical Trials

• Some European studies used 17.5 grams twice daily (35 grams total) of PEG with electrolytes 1
• The largest U.S. trial (304 participants) used 17 grams once daily of PEG 3350 without electrolytes for 6 months with excellent results 1
• Higher doses up to 41.1 grams daily have been studied and found safe, with dose titration allowed based on response 3

The 2023 AGA-ACG guideline strongly recommends PEG for chronic idiopathic constipation (strong recommendation, moderate certainty evidence), making it a first-line osmotic laxative 1.

Pediatric Dosing

For children, the dosing is weight-based rather than a fixed dose:

Maintenance Therapy

• Mean effective dose: 0.8 g/kg/day (range 0.27-1.42 g/kg/day) 4
• Alternative dosing: 1.0-1.5 g/kg/day 5
• Starting dose: 1 g/kg/day, adjusted every 3 days to achieve 2 soft stools daily 4

For Infants (<18 months)

• Mean effective dose: 0.78 g/kg/day (range 0.26-1.26 g/kg/day) 6
• This population has been studied and found safe, though less data exists 6

For Fecal Impaction (Disimpaction)

• 1.0-1.5 g/kg/day for 3 days is effective for treating fecal impaction 7
• Higher doses (1.5 g/kg/day) achieved 95% disimpaction success versus 55% with lower doses 7

Practical Measurement Considerations

Since many families use household measuring devices rather than scales:

• 1 leveled teaspoon ≈ 3.3 grams 8
• 1 leveled tablespoon ≈ 10 grams 8
• 1 capful = 17 grams (manufacturer standard) 2, 8

For pediatric dosing requiring precision, using a kitchen scale is most accurate, but leveled household measuring devices provide reasonable consistency 8.

Dosing Algorithm

1. Adults: Start with 17 grams once daily
2. Children >18 months: Start with 1 g/kg/day (maximum initial dose)
3. Infants <18 months: Start with 0.8 g/kg/day
4. Adjust dose every 3 days based on stool frequency and consistency
5. Target: 2 soft stools per day for children; improvement in spontaneous bowel movements for adults
6. Duration: Can be used safely for at least 6 months in adults 1; long-term use in children has been documented up to 21 months 6

Important Caveats

• Mix powder in 8-10 ounces of liquid (any beverage) 1, 2
• Common side effects include bloating, flatulence, abdominal distension, and diarrhea 1
• No maximum dose is clearly defined, allowing for upward titration if needed 1
• The medication is grit-free and unflavored, improving palatability 2
• Blood levels of ethylene glycol, diethylene glycol, and triethylene glycol remain well below toxic levels even with daily use 9

The evidence strongly supports 17 grams daily as the standard adult dose, with weight-based dosing (approximately 0.8 g/kg/day) for pediatric patients, both allowing for individualized titration based on clinical response.