Initial Dose of Polyethylene Glycol 3350 for a 31-lb Child
For a 31-lb (14-kg) child with constipation, start with 5.6 grams of PEG 3350 once daily (0.4 g/kg/day), mixed in at least 4–8 ounces of liquid. 1
Dosing Calculation and Rationale
The recommended starting dose for pediatric constipation is 0.4 g/kg per day, which has been validated in a multicenter, double-blinded, placebo-controlled trial as the optimal initial dose balancing efficacy and tolerability. 1
For a 14-kg child: 14 kg × 0.4 g/kg = 5.6 grams daily. 1
This dose achieved a 74% treatment success rate (defined as ≥3 bowel movements in the second week) compared to 42% with placebo, with significant improvements in stool consistency and straining. 1
Preparation and Administration
Mix the powder in at least 4–8 ounces of liquid (water, juice, soda, coffee, or tea). 2, 3
Juices containing sorbitol provide a synergistic osmotic effect and may enhance efficacy. 2
Insufficient liquid volume is the most common cause of treatment failure—ensure the child drinks the full volume and maintains adequate fluid intake throughout the day beyond just the mixing liquid. 2, 4
Expected Timeline and Response
The first bowel movement typically occurs within 2–4 days of starting therapy. 3
Continue the initial dose for 1–2 weeks to achieve optimal effect before considering dose adjustment. 2, 4
If no bowel movement occurs after 3–4 days of optimal PEG therapy with confirmed adequate hydration, add a bisacodyl suppository (5 mg for children) or glycerin suppository while continuing PEG. 2
Dose Titration Algorithm
If the 0.4 g/kg dose is insufficient after 2 weeks with confirmed adequate fluid intake, increase to 0.8 g/kg per day (11.2 grams for this 14-kg child). 1
The mean effective maintenance dose in pediatric studies is 0.78–0.84 g/kg per day (range 0.26–1.42 g/kg/day). 5, 6
Adjust the dose every 3 days as needed to achieve 2 soft stools per day, monitoring stool frequency and consistency. 6
Safety Considerations and Monitoring
Common adverse effects include mild abdominal distension, flatulence, nausea, and transient diarrhea, which are generally dose-dependent. 2, 1
At the 0.8 g/kg dose, there is increased risk of abdominal pain and fecal incontinence compared to lower doses. 1
Rule out fecal impaction before starting therapy—if present, manual disimpaction or enema may be required first. 2
Contraindications include bowel obstruction, paralytic ileus, or symptoms of nausea/vomiting with abdominal distention. 3
Maintenance Therapy
Continue PEG once bowel movements normalize rather than stopping abruptly—therapeutic response is durable for 6–12 months in pediatric studies. 2
The average treatment duration in pediatric trials was 8.4 months, with efficacy and safety maintained throughout. 2
For persistent constipation despite optimal PEG dosing, consider adding an oral stimulant laxative (senna 8.6 mg or bisacodyl 5 mg) approximately 30 minutes after meals to exploit the gastro-colonic reflex. 2
Critical Implementation Pitfalls to Avoid
Not confirming adequate total daily fluid intake beyond the mixing liquid—PEG requires water throughout the day to work osmotically. 2, 4
Using insufficient mixing liquid volume—always use at least 4 ounces, preferably 8 ounces. 2, 4
Stopping therapy prematurely—wait the full 2–4 days for initial response and continue 1–2 weeks before declaring treatment failure. 3, 2
Delaying rectal intervention beyond 3–4 days without a bowel movement—this increases risk of worsening impaction. 2