What is the appropriate dose of MiraLAX (polyethylene glycol 3350) for a 3-year-old child weighing 48 pounds with constipation?

MiraLAX Dosing for a 48-Pound 3-Year-Old with Constipation

For a 3-year-old weighing 48 pounds (approximately 22 kg), start with 8.8 grams (0.4 g/kg) of MiraLAX once daily, mixed in at least 4-8 ounces of liquid, and adjust the dose every 3 days based on response to achieve 1-2 soft bowel movements daily. 1, 2

Weight-Based Dosing Calculation

• A 48-pound child weighs approximately 22 kg (48 ÷ 2.2 = 21.8 kg) 2
• The recommended starting dose is 0.4 g/kg/day, which equals approximately 8.8 grams for this child 2
• This dose can be adjusted between 0.2-0.8 g/kg/day (4.4-17.6 grams) based on response, though doses above 0.6 g/kg may increase abdominal pain and fecal incontinence 2, 3
• The average effective maintenance dose across multiple studies is 0.7-0.8 g/kg/day (15-18 grams for this child), allowing for gradual upward titration if needed 1, 3

Critical Administration Instructions

• Mix the powder in at least 4-8 ounces of liquid—insufficient liquid volume is the most common cause of treatment failure 1
• Acceptable liquids include water, juice, coffee, or tea; juices with sorbitol content (like prune or apple juice) provide synergistic osmotic effects 1
• Ensure adequate daily fluid intake beyond just the mixing liquid, as PEG requires water to work osmotically 1, 4
• Adjust the dose every 3 days as needed to achieve 2 soft stools per day 3

Pre-Treatment Assessment

• Rule out fecal impaction by physical examination—if present, manual disimpaction or glycerin suppository may be required first 1
• Exclude bowel obstruction or paralytic ileus before starting therapy 1
• Confirm adequate daily fluid intake capability 1

Expected Response Timeline and Escalation

• Most children respond within 3-4 days with increased bowel movement frequency and softer stool consistency 2, 3
• If no bowel movement occurs after 3-4 days, add a bisacodyl suppository (10 mg) or glycerin suppository while continuing PEG 1, 4
• For persistent constipation beyond this point, consider adding an oral stimulant laxative (senna or bisacodyl) to the PEG regimen 1, 4

Treatment Duration and Maintenance

• Continue maintenance dosing once bowel movements normalize rather than stopping abruptly 1
• PEG is safe and effective for 6-12 months or longer in children, with an average treatment duration of 8.4 months in pediatric studies 1
• The average effective long-term dose is 0.7-0.8 g/kg/day, allowing for gradual dose reduction once response is established 1

Safety Profile and Side Effects

• PEG is well-tolerated with minimal side effects 2, 3, 5
• Transient diarrhea may occur (reported in 9-16% of patients) and typically resolves with dose adjustment 6, 5
• Abdominal distension, flatulence, and nausea are generally mild 1
• Higher doses (0.8 g/kg) are associated with more abdominal pain and fecal incontinence 2

Common Clinical Pitfalls to Avoid

• Inadequate liquid volume (less than 4-8 ounces) significantly reduces efficacy 1, 4
• Not confirming adequate daily fluid intake beyond the mixing liquid leads to treatment failure 1, 4
• Assuming treatment failure without first optimizing dose and ensuring compliance 1
• Delaying rectal intervention beyond 3-4 days without a bowel movement increases fecal impaction risk 1, 4
• Premature discontinuation once symptoms improve—continue maintenance therapy for several months 1