Is lactose (lactose) a suitable treatment for constipation in a 3-month-old infant?

Lactose for Constipation in a 3-Month-Old

Lactose itself is NOT recommended as a treatment for constipation in a 3-month-old infant; instead, use fruit juices containing sorbitol (such as prune, pear, or apple juice) or lactulose if dietary measures fail.

Why Lactose Is Not the Answer

The question appears to conflate lactose with lactulose or sorbitol-containing juices, which are the actual osmotic agents used for infant constipation. Lactose is a naturally occurring sugar in breast milk and standard infant formulas that is typically well-absorbed and does not have laxative properties 1. In fact, lactose intolerance causes diarrhea, not constipation, due to malabsorption creating an osmotic load 1.

Appropriate Treatment Options for a 3-Month-Old

First-Line: Dietary Modifications

• Continue breastfeeding on demand without modification if the infant is breastfed, as this remains the optimal nutrition 2, 3
• For formula-fed infants, consider formulas with high β-palmitate and increased magnesium content to soften stools 4
• Avoid switching from breastfeeding to formula for functional constipation, as this is not recommended 4

Second-Line: Osmotic Agents

• Lactulose (not lactose) is the appropriate osmotic laxative for infants under 6 months 5

  • Initial dosing: 2.5-10 mL daily in divided doses 6
  • Adjust dose to produce 2-3 soft stools daily 6
  • If diarrhea develops, reduce dose immediately and discontinue if it persists 6

• Fruit juices containing sorbitol (prune, pear, apple) can be used as an alternative 1

  • The North American Society of Pediatric Gastroenterology, Hepatology, and Nutrition recommends these juices to increase stool frequency and water content 1
  • Sorbitol is absorbed slowly via passive diffusion, creating an osmotic effect 1
  • Appropriate dosing is 10 mL/kg body weight 1

Third-Line: For Infants Over 6 Months

• Polyethylene glycol (PEG) is authorized and effective for infants over 6 months of age 5, 7
• This is not applicable to your 3-month-old patient but becomes an option as the infant ages

Critical Pitfalls to Avoid

• Do not confuse lactose with lactulose—they are completely different compounds with opposite effects 6
• Do not diagnose lactose intolerance based solely on stool studies (pH or reducing substances) without clinical symptoms of worsening diarrhea 2
• Do not use specialized "anti-constipation" formulas without medical supervision, as evidence for their efficacy is limited 4
• Ensure adequate dosing and duration—underdosing is a common cause of treatment failure, and maintenance therapy may be needed for months 5, 8

When to Suspect Organic Causes

Refer for further evaluation if red flags are present 9, 7:

• Constipation since birth (consider Hirschsprung's disease) 9
• Failure to pass meconium within 48 hours of birth
• Ribbon-like stools or explosive passage of stool
• Poor growth or developmental delays
• Abnormal neurological examination or absent anal wink reflex