What is the recommended dose of lactulose for a 3-month-old, 6 kg infant?

Lactulose Dosing for a 3-Month-Old Infant

For a 3-month-old, 6 kg infant with constipation, start with lactulose 2.5-10 mL daily in divided doses, titrating to achieve 2-3 soft stools per day. 1

Initial Dosing Strategy

• The FDA-approved initial daily oral dose for infants is 2.5-10 mL in divided doses, with the goal of producing 2-3 soft stools daily 1
• For a 6 kg infant, a reasonable starting dose would be 5 mL daily (approximately 3.3 g lactulose), divided into 2-3 doses (e.g., 2.5 mL twice daily or 1.7 mL three times daily) 1
• Lactulose is authorized and effective for infants under 6 months of age, making it appropriate for this 3-month-old patient 2

Dose Titration and Monitoring

• If the initial dose causes diarrhea, reduce the dose immediately 1, 3
• If diarrhea persists despite dose reduction, discontinue lactulose to prevent dehydration and electrolyte disturbances 1, 3
• Titrate the dose every 1-2 days based on stool frequency and consistency, aiming for 2-3 soft stools daily 1
• The maximum dose used in pediatric studies for disimpaction is 4-6 mL/kg/day (maximum 120 mL/day), though this is typically reserved for fecal impaction rather than routine constipation 4

Critical Safety Considerations

• Excessive lactulose can cause dehydration, hypernatremia, and severe perianal skin irritation in infants, emphasizing the need for careful dose management 3
• Monitor for aspiration risk if excessive diarrhea occurs, as this increases the danger of aspiration 3
• The misconception that larger doses are needed for lack of effect is dangerous—instead, search for other causes or consider alternative therapies if standard dosing fails 3

Practical Administration

• Lactulose solution typically contains 10 g lactulose per 15 mL (approximately 667 mg/mL) 1
• For a 5 mL daily dose: administer 2.5 mL twice daily, which provides approximately 3.3 g lactulose total 1
• Can be mixed with water, milk, or fruit juice to improve palatability 1

When to Escalate or Change Therapy

• If no response after 48-72 hours at appropriate doses, reassess for underlying causes rather than automatically increasing the dose 3
• For fecal impaction specifically, higher doses (4-6 mL/kg/day) may be used for disimpaction, followed by reduction to maintenance dosing 4
• Polyethylene glycol (PEG) is an alternative for infants over 6 months if lactulose is ineffective or poorly tolerated 2