Miralax Dosing for a 9-Year-Old Child Weighing 37 kg
For a 9-year-old boy weighing 37 kg with constipation, start with 0.5 to 0.8 grams per kilogram per day of polyethylene glycol (PEG) 3350, which translates to approximately 17 to 30 grams daily (one capful to approximately 1.5 capfuls of Miralax powder mixed in 8 ounces of water). 1, 2, 3
Practical Dosing Strategy
- Initial dose: Begin with 17 grams (one capful) once daily, as this is the standard adult dose and is appropriate for a child of this weight 1, 4
- Dose adjustment: If constipation persists after 3-5 days, increase to 0.8-1.0 g/kg/day (approximately 30-37 grams daily, or about 1.5 to 2 capfuls) 3
- Maintenance dosing: Once regular bowel movements are established, the effective maintenance dose typically ranges from 0.78 g/kg/day (approximately 29 grams for this child) 3
Evidence Supporting This Approach
- PEG 3350 is the laxative of first choice for functional constipation in children according to international guidelines, effective for both disimpaction and maintenance treatment 2
- Studies demonstrate that PEG is highly effective with a good safety profile in pediatric patients, with efficacy being dose-dependent 2, 5
- Research in children shows mean effective maintenance doses of 0.78 g/kg/day with a range of 0.26-1.26 g/kg/day, confirming safety and efficacy across this dosing spectrum 3
Administration Details
- Mix the powder thoroughly in 8 ounces of water or other beverage 1
- Can be given once daily or divided into two doses if better tolerated 2
- Administer with adequate fluid intake to optimize osmotic effect 2
Monitoring and Adjustment
- Expect increased stool frequency within 24-48 hours of starting therapy 4
- Minor adverse events may include transient diarrhea (resolves with dose adjustment) or mild flatulence 3
- If diarrhea occurs, reduce the dose; if constipation persists after one week at maximum dose, consider alternative or adjunctive therapies 2, 5
Safety Considerations
- PEG has been reported as safe in children, though patients predisposed to water and electrolyte imbalances should have serum electrolytes monitored 2
- Only minor adverse events have been reported in pediatric studies, with excellent tolerability 2, 5
- Treatment duration can be extended as needed for chronic constipation, with studies showing safe use for months 3