What is the preferred treatment between peg (polyethylene glycol) and lactulose for constipation?

PEG vs Lactulose for Constipation

Polyethylene glycol (PEG) should be used preferentially over lactulose for the treatment of chronic constipation in both adults and children. 1

Strength of Recommendation

The 2023 American Gastroenterological Association-American College of Gastroenterology guidelines provide a strong recommendation with moderate certainty of evidence for PEG (Recommendation 2), while lactulose receives only a conditional recommendation with very low certainty of evidence (Recommendation 4) and is positioned as a second-line agent for patients who fail or are intolerant to over-the-counter therapies like PEG. 1

Comparative Efficacy

PEG demonstrates superior efficacy across multiple outcomes:

• Stool frequency: PEG increases complete spontaneous bowel movements (CSBMs) by 2.90 per week and spontaneous bowel movements (SBMs) by 2.30 per week compared to placebo, with durable response over 6 months. 1

• Head-to-head comparison: Direct comparative trials show PEG is more effective than lactulose for stool frequency per week, stool form, relief of abdominal pain, and reduces the need for additional laxative products. 2

• Response rates: PEG achieves a 3.13-fold higher responder rate compared to placebo (312 more responders per 1,000 patients). 1

• Symptom relief: PEG provides better global symptom relief (454 more per 1,000 achieving relief) and improvements in stool form and straining compared to lactulose. 1

Side Effect Profile

PEG has a more favorable tolerability profile:

• PEG causes less flatulence and bloating compared to lactulose, which undergoes extensive fermentation in the colon. 3

• Common PEG side effects (abdominal distension, loose stool, flatulence, nausea) are generally mild to moderate and dose-dependent. 1

• Lactulose's major limitation: Bloating and flatulence are dose-dependent and common with lactulose, which may significantly limit its use in clinical practice. 1

• In a direct comparison study, flatus was less frequently reported in the PEG group, and PEG was better tolerated overall. 3

Dosing and Practical Use

PEG dosing:

• Standard dose: 17 g daily mixed in 8 ounces of liquid (water, juice, coffee, or tea). 1
• Can be titrated from 1-3 doses daily based on response. 3
• Average effective dose: 1.6 sachets/day. 3

Lactulose dosing:

• Typical dose: 10-20 g daily, often requiring higher doses (average 2.1 sachets/day) to achieve similar efficacy to PEG. 3

Treatment Algorithm

Follow this stepwise approach:

1. First-line: Start with PEG 17 g daily (can consider fiber supplementation for mild constipation before or in combination with PEG). 1

2. Titration: Adjust PEG dose (1-3 doses daily) based on response over 2-4 weeks. 4

3. Second-line: Consider lactulose only if patient fails or is intolerant to PEG. 1

4. Combination therapy: If inadequate response to PEG alone, add agents with different mechanisms (e.g., linaclotide) rather than switching to lactulose. 4

Special Populations

Elderly patients:

• PEG (17 g/day) offers an efficacious and tolerable solution with a good safety profile for elderly patients. 1
• Particularly important for those with cardiac or renal comorbidities where monitoring is needed. 1

Pediatric patients:

• PEG is more effective than lactulose in children for stool frequency, stool form, and abdominal pain relief. 2
• For fecal impaction in children, both agents achieve disimpaction, but PEG shows significantly faster response. 5
• Lactulose may be considered as an alternative in resource-limited settings due to lower cost. 5

Cost and Accessibility

PEG advantages:

• Widely available over-the-counter without prescription. 1
• Relatively inexpensive despite being more costly than lactulose. 4
• The superior efficacy and tolerability justify any modest cost difference. 3, 6

Key Pitfalls to Avoid

• Don't start with lactulose first: The evidence clearly supports PEG as first-line therapy; lactulose should be reserved for PEG failures. 1

• Ensure adequate hydration: PEG requires sufficient fluid intake (at least 8 ounces with each dose) to work effectively. 1, 7

• Don't underdose PEG: Start with the full 17 g dose rather than titrating up slowly, as this delays therapeutic response. 1

• Recognize lactulose's fermentation effects: The bloating and gas from lactulose fermentation often leads to poor adherence and treatment failure. 1, 3