What is the recommended dose of lactulose (osmotic laxative) syrup for pediatric constipation?

Pediatric Lactulose Dosing for Constipation

For infants, start with 2.5-10 mL daily in divided doses; for older children and adolescents, use 40-90 mL daily in divided doses, with the goal of producing 2-3 soft stools per day. 1

Age-Specific Dosing Recommendations

Infants (< 1 year)

• Initial dose: 2.5-10 mL daily in divided doses 1
• Adjust dose based on stool frequency and consistency 1
• If diarrhea develops, reduce dose immediately and discontinue if it persists 1

Older Children and Adolescents

• Total daily dose: 40-90 mL in divided doses 1
• Target outcome: 2-3 soft stools daily 1
• Dose adjustments should be made every 1-2 days based on response 1

Critical Dosing Principles

The FDA label provides the only pediatric-specific dosing guidance available, as major gastroenterology guidelines focus exclusively on adult populations. 2 The 2023 AGA/ACG guidelines studied lactulose only in elderly adults and provide no pediatric recommendations. 2

Dose Titration Strategy

• Start at the lower end of the dosing range 1
• Increase gradually every 1-2 days until achieving 2-3 soft stools daily 1
• Immediately reduce dose if diarrhea occurs 1
• Discontinue if diarrhea persists despite dose reduction 1

Important Clinical Considerations

Side Effect Management

• Bloating and flatulence are dose-dependent and occur in approximately 20% of patients 3
• Abdominal pain and cramping are common adverse effects that may limit use 3
• Starting at lower doses and titrating upward minimizes gastrointestinal side effects 3

Comparative Effectiveness Evidence

PEG 3350 demonstrates superior efficacy compared to lactulose in pediatric constipation. 4 In a randomized controlled trial of 91 children, PEG 3350 achieved 56% success rate versus 29% with lactulose, with fewer side effects including less abdominal pain, straining, and pain at defecation. 4 PEG 3350 required lower weight-based dosing (0.26 g/kg) compared to lactulose (0.66 g/kg). 4

When to Consider Lactulose

• Lactulose remains a reasonable option when PEG is unavailable or not tolerated 5
• It is significantly less expensive and more widely available than PEG preparations 5
• Both agents achieved successful disimpaction in 100% of children by day 7, though PEG showed faster response 5

Common Pitfalls to Avoid

Underdosing

• Fixed, inadequate dosing without titration is a major cause of treatment failure 6
• Only 5% of primary care physicians instruct parents to adjust doses based on response 6
• Nearly 40% of children remain symptomatic after 2 months when undertreated 6

Lack of Disimpaction

• Children requiring disimpaction followed by daily maintenance therapy have better outcomes than those receiving only daily laxatives 6
• For disimpaction, higher doses of 4-6 mL/kg/day (maximum 120 mL/day) may be used for up to 6 days 5

Electrolyte Monitoring

• Monitor potassium levels in patients receiving high-dose lactulose, especially those on diuretics or with renal impairment 3
• Excessive dosing can cause hypokalemia and hypernatremia 3

Practical Implementation Algorithm

1. Assess for fecal impaction - if present, use higher disimpaction doses (4-6 mL/kg/day up to 120 mL/day for up to 6 days) 5

2. Initiate maintenance therapy:

   • Infants: Start 2.5-5 mL daily divided 1
   • Children/adolescents: Start 40 mL daily divided 1

3. Titrate every 1-2 days until achieving 2-3 soft stools daily 1

4. If inadequate response after 2-4 weeks at maximum tolerated dose or intolerable bloating, switch to PEG 3350 4

5. Monitor for diarrhea and reduce dose immediately if it occurs 1