What is the recommended dosage of MiraLAX (polyethylene glycol 3350) for pediatric patients with constipation?

MiraLAX Dosing for Pediatric Constipation

For pediatric functional constipation, start with 0.4 g/kg/day of polyethylene glycol 3350 (MiraLAX) mixed in at least 4-8 ounces of liquid, adjusting the dose between 0.2-0.8 g/kg/day based on response. 1

Initial Dosing Strategy

• Begin with 0.4 g/kg/day as the optimal starting dose for children with functional constipation, as this dose demonstrates the best balance of efficacy and tolerability 1
• Lower doses of 0.2 g/kg/day are effective but may require upward titration 1
• Higher doses of 0.8 g/kg/day increase the risk of abdominal pain and fecal incontinence without significantly improving outcomes 1
• The typical maintenance dose averages 0.78-0.84 g/kg/day (range 0.26-1.42 g/kg/day) 2, 3

Age-Specific Considerations

• For infants younger than 18 months, PEG 3350 is safe and effective at a mean maintenance dose of 0.78 g/kg/day, with similar safety profiles to older children 3
• Limited data exists for infants under 6 months, though small case series show efficacy at similar weight-based dosing 3
• The American Gastroenterological Association cautions against stimulant laxatives as first-line therapy in infants due to unknown long-term safety 4

Critical Administration Requirements

• Mix the powder in at least 4-8 ounces of liquid—insufficient volume is the most common cause of treatment failure 5
• Acceptable liquids include water, juice, coffee, or tea 5
• Juices containing sorbitol (prune, pear, apple) provide synergistic osmotic effects and are particularly useful 5, 4
• Ensure adequate daily fluid intake beyond just the mixing liquid, as PEG requires water to work osmotically 5, 6

Dose Titration Protocol

• Adjust the dose every 3 days as needed to achieve 2 soft stools per day 2
• Target stool frequency of ≥3 bowel movements per week with soft consistency 1
• If no bowel movement occurs after 3-4 days, add a bisacodyl suppository (10mg) or glycerin suppository while continuing PEG 5, 6
• For persistent constipation despite optimal PEG dosing, consider adding an oral stimulant laxative (senna or bisacodyl) to the regimen 5, 6

Expected Outcomes and Duration

• Stool frequency typically increases from 2-3 per week to 15-17 per week during treatment 2
• Stool consistency improves significantly at doses of 0.4 g/kg or higher 1
• In children with encopresis, soiling events decrease from approximately 10 per week to 1-2 per week 2
• Continue maintenance dosing once bowel movements normalize rather than stopping abruptly 5
• Treatment response is durable over 6 months in adults, suggesting similar long-term efficacy in children 5

Safety Profile and Adverse Effects

• PEG 3350 is well tolerated with minimal adverse effects 1, 2, 3
• Transient diarrhea may occur but typically resolves with dose adjustment 3
• Abdominal distension, flatulence, and nausea are generally mild 5
• Higher doses (0.8 g/kg/day) increase the risk of abdominal pain and fecal incontinence 1

Pre-Treatment Assessment

• Rule out bowel obstruction or paralytic ileus before initiating therapy 5
• Check for fecal impaction, which may require manual disimpaction or enema before starting PEG 5
• Avoid sodium phosphate preparations in young children due to risk of electrolyte abnormalities and mucosal injury 4
• Use magnesium-based laxatives with caution in patients with renal concerns 4

Common Clinical Pitfalls to Avoid

• Inadequate liquid volume (less than 4-8 ounces) significantly reduces efficacy 5, 6
• Not confirming adequate daily fluid intake beyond the mixing liquid leads to treatment failure 5, 6
• Assuming treatment failure without first optimizing dose and ensuring compliance 5, 6
• Delaying rectal intervention beyond 3-4 days without a bowel movement increases fecal impaction risk 5, 6
• Stopping therapy prematurely once symptoms improve rather than continuing maintenance dosing 5

Adjunctive Measures

• Address underlying constipation with dietary modifications, including increased fluids and fiber if adequate fluid intake is ensured 5
• Encourage regular toileting habits, especially after meals 5
• For mild, recent-onset constipation, sorbitol-containing juices (2-4 oz daily) may be sufficient before escalating to PEG 4