MiraLAX Dosing in Young Children
The FDA-approved labeling states that polyethylene glycol 3350 (MiraLAX) should not be used by children, and the product is not approved for pediatric use. 1
However, substantial research evidence demonstrates that PEG 3350 can be safely used off-label in infants and young children under medical supervision, with specific weight-based dosing guidelines established through clinical studies.
Off-Label Use: Evidence-Based Age and Dosing Guidelines
Minimum Age for Use
Research supports the safe use of PEG 3350 in infants as young as 1 month of age, with multiple studies documenting efficacy and safety in children under 18 months. 2, 3
The effective maintenance dose for infants under 18 months is approximately 0.78 g/kg/day (range 0.26-1.26 g/kg/day), based on a study of 28 patients aged 0-17 months. 2
For children under 2 years of age, the mean effective dose is 0.8-1.1 g/kg/day, with short-term dosing averaging 1.1 g/kg/day and long-term maintenance at 0.8 g/kg/day. 3
Calculating 1/3 Scoop Dosing
One full scoop of MiraLAX contains 17 grams of PEG 3350, so 1/3 of a scoop equals approximately 5.7 grams. 1
For a 5.7-gram dose to be appropriate, the child would need to weigh approximately 7-8 kg (15-18 lbs) based on the 0.78 g/kg/day maintenance dosing. 2
This weight typically corresponds to infants aged 6-9 months, though individual growth patterns vary. 2
Safety Profile in Young Children
PEG 3350 relieved constipation in 97.6% of infants under 18 months, with minimal side effects limited to transient diarrhea (4 patients) and increased gas (1 patient), all resolving with dose adjustment. 2
In children under 2 years, constipation was relieved in 85% with short-term therapy and 91% with long-term therapy, with no subjects discontinuing due to adverse effects. 3
The most common adverse effect is diarrhea, which resolves by lowering the dose—no serious electrolyte disturbances were documented in real-world use of PEG 3350 with electrolytes in 13,235 children under 2 years. 3, 4
Critical Clinical Considerations
Contraindications and Warnings
Do not use in children with symptoms of bowel obstruction (nausea, vomiting, abdominal pain or distention), as this is an absolute contraindication. 1
The FDA label explicitly states the product should not be used by children, so any pediatric use must be under physician supervision and represents off-label prescribing. 1
Avoid use in pregnant women unless prescribed by a physician, though this is less relevant for pediatric dosing questions. 1
Dose Titration Strategy
Start with 0.8-1.0 g/kg/day and adjust every 3 days to achieve 1-2 soft, painless stools per day. 3, 5
Parents should be instructed to adjust the dose based on stool frequency and consistency, aiming for a stool consistency rating of 3-4 on a 5-point scale (where 1 is hard and 5 is watery). 5
The first bowel movement typically occurs within 2-4 days, though individual response varies. 1
Duration of Therapy
Initial treatment courses typically last 1-2 weeks for acute constipation, after which lifestyle modifications should be implemented. 1
Long-term maintenance therapy is safe and effective, with mean treatment duration of 6.2 months in infants and 11 months in toddlers documented without significant adverse effects. 2, 3
Do not continue therapy beyond 2 weeks without physician guidance, as the FDA-approved indication is for up to 2 weeks of use. 1
Administration Recommendations
Mix the powder in 4-8 oz of water, juice, soda, coffee, or tea until fully dissolved before administration. 1
For infants who cannot drink from a cup, the solution can be given via bottle or syringe in smaller volumes with adequate fluid. 2
Measure doses carefully using the provided dosing cup or a calibrated measuring device—one heaping tablespoon approximates 17 grams but is less precise than the scoop. 1