What is the appropriate dosing of MiraLAX (polyethylene glycol 3350) for a 12-month-old infant?

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Last updated: November 9, 2026 • View editorial policy

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MiraLAX Dosing for 12-Month-Old Infants

For a 12-month-old infant with functional constipation, start MiraLAX (polyethylene glycol 3350) at 0.8 g/kg/day for maintenance therapy, which can be titrated to achieve 1-2 soft, painless stools daily.

Evidence-Based Dosing Recommendations

Maintenance Therapy

The most robust pediatric data for infants comes from studies specifically evaluating children under 18 months of age. The effective maintenance dose is 0.78-0.8 g/kg/day 1, 2. For a typical 12-month-old weighing approximately 10 kg, this translates to roughly 8 grams (approximately half a standard 17g adult dose) once daily.

  • Start at 0.8-1.0 g/kg/day mixed in 4-8 ounces of liquid
  • Titrate dose based on response to achieve 1-2 soft stools daily
  • Maximum studied dose in this age group: 1.26 g/kg/day 1
  • Duration: Safe for extended use (mean 6-11 months in studies) 1, 2

Efficacy and Safety Profile

PEG 3350 demonstrates excellent efficacy in infants, with constipation relief in 85-97% of patients under 18 months 1, 2. The safety profile is favorable:

  • Most common side effect: Transient diarrhea (resolves with dose adjustment)
  • Minimal adverse events: One study reported increased gas in 1/28 patients and transient diarrhea in 4/28 patients 1
  • No severe clinical or biochemical adverse events in controlled trials 3
  • No electrolyte disturbances reported in real-world cohort of over 13,000 children under 2 years 4

Practical Implementation

Dosing Algorithm

  1. Calculate weight-based dose: 0.8 g/kg/day as starting point
  2. Mix thoroughly in any beverage (4-8 oz for infants)
  3. Assess response after 2-3 days:
    • If inadequate response: Increase by 0.1-0.2 g/kg/day
    • If diarrhea develops: Decrease dose by 0.1-0.2 g/kg/day
  4. Target: 1-2 soft, painless bowel movements daily

Important Caveats

  • Off-label use: MiraLAX is FDA-approved only for adults 17+ years for occasional constipation 5, but extensive pediatric data supports its use in infants
  • Measurement precision: Use accurate measuring devices (oral syringe) rather than household spoons for this age group
  • Hydration: Ensure adequate fluid intake alongside PEG therapy
  • Duration: Can be used long-term (6-12+ months) as needed 1, 2

When to Adjust or Escalate

  • If no response after 1 week at maximum dose (1.2 g/kg/day), consider evaluation for underlying causes
  • Persistent symptoms despite optimal dosing warrant gastroenterology referral
  • Avoid combining with other osmotic laxatives initially

The evidence strongly supports PEG 3350 as first-line therapy for functional constipation in 12-month-olds, with a well-established safety profile and superior efficacy compared to alternative treatments 3.

References

1
Research

Polyethylene glycol for constipation in children younger than eighteen months old.

Journal of pediatric gastroenterology and nutrition, 2004

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.