Pediatric Dosing of MiraLAX (Polyethylene Glycol 3350)
For pediatric constipation, start MiraLAX at 0.8 g/kg/day (approximately 1 capful or 17g for a 20kg child) mixed in 4-8 ounces of liquid, adjusting the dose every 3 days to achieve 1-2 soft, painless stools daily.
Age-Specific Dosing Guidelines
Infants and Toddlers (<2 years)
- Initial dose: 0.8-1.0 g/kg/day mixed in liquid 1, 2
- Effective maintenance dose: 0.78-0.8 g/kg/day (range 0.26-1.26 g/kg/day) 1, 2
- Safe and effective even in infants as young as 1 month, with 97.6% achieving constipation relief 1
- Duration of therapy averages 6-11 months with excellent tolerability 1, 2
Children 2-18 Years
- Initial dose: 1 g/kg/day (maximum starting dose) 3
- Effective maintenance dose: 0.8-0.84 g/kg/day (range 0.27-1.42 g/kg/day) 3, 4
- Adjust dose every 3 days based on response to achieve target of 2 soft stools daily 3
Bowel Preparation (Colonoscopy)
- 1.5 g/kg/day for 4 days before the procedure, with clear liquid diet on day 4 5
- Alternative 1-day preparations are also effective, though less studied 5
Practical Administration
Mixing Instructions
- Mix powder in at least 4-8 ounces of liquid 6
- Acceptable liquids include water, juice (prune, pear, apple, white grape), coffee, or tea 6
- Juices with sorbitol content (prune, pear, apple) provide synergistic osmotic effect 6
- Critical pitfall: Insufficient liquid volume is a common cause of treatment failure 6
Dose Titration Algorithm
- Days 1-3: Start at 0.8-1.0 g/kg/day 3, 1, 2
- Day 3 assessment: If no bowel movement or stool remains hard, increase dose by 0.2 g/kg/day 3
- Continue adjusting every 3 days until achieving 1-2 soft, painless stools daily 3, 2
- If diarrhea occurs: Reduce dose immediately; this is the only significant adverse effect reported 4, 1, 2
Expected Outcomes and Duration
Efficacy Metrics
- Stool frequency increases from baseline 2.3 to 16.9 stools per week 3
- Stool consistency improves from hard (score 1.2) to soft-formed (score 3.3) 3
- Soiling decreases from 10 to 1.3 episodes per week in children with encopresis 3
- 85-97% success rate across all pediatric age groups 1, 2
Treatment Duration
- Response is durable over 6 months in adults, suggesting similar long-term efficacy in children 5
- Average pediatric treatment duration is 6-11 months, though some require longer therapy 1, 2
- Continue maintenance dosing once bowel movements normalize rather than stopping abruptly 7
Safety Profile
Adverse Effects
- Diarrhea is the primary side effect (9-32% of patients), resolving with dose reduction 3, 4, 1, 2
- Abdominal distension, flatulence, and nausea may occur but are generally mild 5
- No significant adverse effects reported in infants as young as 1 month 1
- No electrolyte abnormalities with PEG 3350 without electrolytes 8, 1, 2
Contraindications and Precautions
- Rule out bowel obstruction or paralytic ileus before initiating therapy 7
- Check for fecal impaction, which may require manual disimpaction or enema first 7
- Ensure adequate daily fluid intake beyond just the mixing liquid, as PEG requires water to work osmotically 6
When to Add Rectal Therapy
Escalation Algorithm
- Days 1-3: Continue PEG 3350 at prescribed dose 7
- Day 3-4 without bowel movement: Add bisacodyl suppository (10mg) or glycerin suppository while continuing PEG 7
- Persistent constipation: Consider adding oral stimulant laxative (senna or bisacodyl) to PEG regimen 7
Common Clinical Pitfalls
Dosing Errors
- Underdosing: Many clinicians start too low; the effective dose is typically 0.8 g/kg/day, not 0.5 g/kg/day 3, 1, 2
- Inadequate liquid volume: Mixing with less than 4 ounces reduces efficacy significantly 6
- Premature discontinuation: Stopping therapy before 6 months often leads to recurrence 1, 2