What is the safety of polyethylene glycol 3350 (PEG 3350) in infants?

Safety of PEG 3350 in Infants

PEG 3350 is not FDA-approved for use in infants, as the drug label explicitly states "Safety and effectiveness in pediatric patients has not been established" 1. However, research evidence demonstrates that PEG 3350 appears safe and effective when used off-label in infants and toddlers under 2 years of age.

Critical FDA Labeling Caveat

The FDA label clearly indicates that pediatric safety has not been established 1. This means any use in infants represents off-label prescribing, which requires careful informed consent discussion with parents about the lack of FDA approval for this age group.

Research Evidence in Infants

Despite the FDA labeling, multiple studies have evaluated PEG 3350 specifically in infants:

Efficacy and Safety Profile

Two key studies from 2004 demonstrate that PEG 3350 appears safe in infants as young as 1 month of age:

• In 75 children under 2 years (mean age 17 months, range 1-24 months), PEG relieved constipation in 85% short-term and 91% long-term at a mean dose of 0.8-1.1 g/kg/day 2

• In 28 patients under 18 months (including 3 infants aged 0-5 months), PEG relieved constipation in 97.6% at a mean maintenance dose of 0.78 g/kg/day 3

Adverse Events

Side effects were consistently mild across studies:

• Transient diarrhea (resolved with dose adjustment) 2, 3
• Increased gas 3
• No severe clinical or biochemical adverse events 4
• No patients discontinued due to adverse effects 2

Dosing in Infants

The research suggests:

• Starting dose: approximately 0.8-1.0 g/kg/day 2, 3
• Adjust dose to achieve 1-2 soft, painless stools daily
• Duration studied ranged from 3 weeks to 21 months 3

Important Clinical Considerations

Electrolyte Concerns

The FDA label warns that "prolonged, frequent or excessive use may result in electrolyte imbalance" 1. While the research studies found no biochemical adverse events 4, this theoretical risk is particularly relevant in infants due to:

• Smaller total body water volume
• Immature renal function
• Greater susceptibility to dehydration

Practical Pitfalls to Avoid

• Do not use in infants with signs of bowel obstruction (nausea, vomiting, abdominal distention) 1
• Monitor for excessive diarrhea which could lead to dehydration and electrolyte disturbances
• Ensure adequate fluid intake when administering PEG 1
• Consider shorter treatment courses initially rather than prolonged use given lack of FDA approval

Clinical Algorithm for Infant Constipation

When considering PEG 3350 in infants:

1. Confirm functional constipation - rule out organic causes (Hirschsprung disease, hypothyroidism, anatomic abnormalities)

2. Try conservative measures first - dietary modifications, adequate fluid intake (though evidence for this is limited in infants)

3. If pharmacologic treatment needed:

   • Discuss off-label status with parents
   • Start at 0.8 g/kg/day
   • Titrate to achieve 1-2 soft stools daily
   • Monitor closely for diarrhea and dehydration

4. Follow-up within 2-4 weeks to assess response and side effects

Bottom Line

While PEG 3350 lacks FDA approval for pediatric use and specifically has not been established as safe in infants per the drug label 1, the available research evidence from multiple studies suggests it is effective and appears safe when used at approximately 0.8-1.0 g/kg/day in infants as young as 1 month 2, 3, 4. The key safety concern is the theoretical risk of electrolyte imbalance with prolonged use, which requires clinical vigilance but was not observed in published studies. Parents must be informed of the off-label nature of this use.