What is the recommended dosage of Miralax (polyethylene glycol) for pediatric constipation?

Pediatric Miralax Dosage for Constipation

For pediatric constipation, start polyethylene glycol 3350 (Miralax) at 1 g/kg/day for infants and toddlers under 2 years, or 17 g daily (one capful) for older children, titrating upward based on response to achieve 1-2 soft, painless stools daily. 1, 2

Age-Specific Dosing Recommendations

Infants and Toddlers (<2 years)

• Start at 1 g/kg body weight per day mixed in any liquid 2
• Titrate to achieve 1-2 soft, painless stools daily 2
• Mean effective dose in clinical studies: 1.1 g/kg/day short-term, 0.8 g/kg/day long-term 2
• Constipation relief achieved in 85% at short-term follow-up (2 months) and 91% at long-term follow-up (11 months) 2

Children ≥2 years

• Start at 17 g daily (one capful mixed in 8 oz water) 1, 3
• This aligns with standard adult dosing for older children 1
• Average effective dose in school-age children: 0.63 g/kg/day 4

Dose Titration Strategy

• Allow 24-48 hours or longer before increasing the dose, as improvement may be delayed 5
• Adjust upward gradually based on stool frequency and consistency 2
• No clear maximum dose exists—titrate to symptom response and side effects 1, 3
• Goal: one soft, non-forced bowel movement every 1-2 days 5

Mechanism and Efficacy

• PEG 3350 acts as an osmotic laxative, trapping water in the intestine and increasing stool bulk 1
• Efficacy is dose-dependent 6
• International guidelines designate PEG as the first-choice laxative for both disimpaction and maintenance treatment in pediatric functional constipation 6
• Response is durable over 6 months 1, 3

Safety Profile and Side Effects

• Highly effective with a good safety profile and well-tolerated by children 6
• Most common adverse effect: diarrhea (reported in 9/46 patients in one study), which resolves with dose reduction 4, 2
• Other common side effects: bloating, abdominal discomfort, and cramping 1, 3
• No subjects stopped PEG due to adverse effects in infant/toddler studies 2
• Only minor adverse events reported overall 6

Important Clinical Considerations

Hydration

• Ensure adequate hydration as PEG intake increases 1, 5

Monitoring

• In patients predisposed to water and electrolyte imbalances, consider monitoring serum electrolytes 6

Persistent Constipation

• If constipation persists despite adequate PEG dosing, add bisacodyl 5-10 mg daily as rescue therapy for children old enough for tablets 3
• For younger children, consider glycerin suppositories or enemas as adjunct therapy 7
• Rule out fecal impaction before escalating maintenance therapy 3

Adjunctive Measures

• Address underlying triggers: adequate fluid intake, physical activity, dietary factors 5
• Consider behavioral interventions and scheduled toilet sitting for toilet-trained children 5

Comparison to Other Laxatives

• PEG is superior to lactulose in terms of tolerability—lactulose causes more bloating and flatulence 1, 3
• Stimulant laxatives (senna, bisacodyl) are recommended for short-term use (≤4 weeks) or rescue therapy only, not first-line maintenance 1, 8
• Fiber preparations and probiotics serve as adjunct therapies in specific scenarios but are not first-line 7

Practical Administration

• Tasteless powder that can be mixed with any liquid, improving compliance 4
• Nonaddictive 4
• Can be used long-term safely for maintenance therapy 6, 2