MiraLAX (Polyethylene Glycol 3350) Pediatric Dosing
For pediatric constipation, start MiraLAX at 0.8 g/kg/day (approximately 1 capful or 17g per 20kg child) mixed in at least 4-8 ounces of liquid, adjusting the dose every 3 days to achieve 1-2 soft, painless stools daily. 1
Initial Dosing by Age and Weight
Standard Maintenance Dosing
- Starting dose: 0.8-1.0 g/kg/day for all pediatric ages 1, 2
- Effective maintenance dose: Typically 0.78-0.84 g/kg/day based on clinical response 3, 4, 2
- Dose range: 0.27-1.42 g/kg/day depending on individual response 2
Age-Specific Considerations
- Infants <18 months: Mean effective dose 0.78 g/kg/day (range 0.26-1.26 g/kg/day) 4
- Toddlers <2 years: Mean effective dose 0.8 g/kg/day, with short-term dosing at 1.1 g/kg/day and long-term at 0.8 g/kg/day 3
- Children ≥2 years: Mean effective dose 0.84 g/kg/day (range 0.27-1.42 g/kg/day) 2
Administration Guidelines
Mixing Instructions
- Mix powder in at least 4-8 ounces of liquid (water, juice, coffee, or tea) 1
- Juices with sorbitol content (like prune or apple juice) provide synergistic osmotic effect 1
- Insufficient liquid volume is the most common cause of treatment failure 1
Dose Titration
- Adjust dose every 3 days to achieve 1-2 soft, painless stools daily 1, 2
- Target stool consistency: Soft but formed (not watery) 2
- If diarrhea occurs: Reduce dose immediately; this is the only common adverse effect 3, 4
Special Clinical Situations
Bowel Preparation (Pre-Procedure)
- Dose: 1.5 g/kg/day for 4 days before procedure 1
- Day 4: Clear liquid diet only 1
- Alternative: 1-day preparations are effective but less studied 1
Dysfunctional Elimination with Constipation
- Average effective dose: 0.63 g/kg/day 5
- Expected outcomes: 85-91% resolution of constipation with improvement in voiding symptoms 5, 3
Critical Safety Checks Before Starting
Mandatory Pre-Treatment Assessment
- Rule out bowel obstruction or paralytic ileus before initiating therapy 1
- Check for fecal impaction: May require manual disimpaction or enema first 1
- Ensure adequate baseline fluid intake: PEG requires water to work osmotically 1
When to Add Rectal Therapy
- If no bowel movement after 3-4 days: Add bisacodyl suppository (10mg) or glycerin suppository while continuing PEG 1
- For persistent constipation: Consider adding oral stimulant laxative (senna or bisacodyl) to PEG regimen 1
Expected Outcomes and Duration
Treatment Response
- Stool frequency: Increases from ~2-3 stools/week to 15-17 stools/week 2
- Time to response: Typically within first week of therapy 3, 2
- Long-term efficacy: Response is durable over 6 months in adults, with similar efficacy expected in children 1
Maintenance Strategy
- Continue dosing once bowel movements normalize rather than stopping abruptly 1
- Mean treatment duration: 6-11 months in clinical studies 3, 4
Common Clinical Pitfalls to Avoid
Dosing Errors
- Inadequate liquid volume reduces efficacy significantly 1
- Not confirming adequate daily fluid intake beyond mixing liquid leads to treatment failure 1
- Assuming treatment failure without first optimizing dose and ensuring compliance leads to premature discontinuation 1
Timing Errors
- Delaying rectal intervention beyond 3-4 days increases risk of fecal impaction 1
- Stopping therapy too early when symptoms improve rather than continuing maintenance 1
Adverse Effects
Common and Manageable
- Diarrhea: Most common adverse effect (reported in 9-32% of patients), resolves with dose reduction 5, 3, 4
- Abdominal distension, flatulence, nausea: Generally mild 1
- No significant adverse effects requiring discontinuation in clinical studies 3, 4, 2