Polyethylene Glycol vs Lactulose for Chronic Constipation
Polyethylene glycol (PEG) should be used as first-line therapy over lactulose for adults with chronic constipation. 1, 2
Strength of Recommendation
The 2023 AGA-ACG joint clinical practice guideline provides a strong recommendation for PEG with moderate certainty evidence, while lactulose receives only a conditional recommendation. 1 This distinction is critical—the guideline panel explicitly prioritized PEG over lactulose based on systematic review of efficacy, tolerability, and patient-centered outcomes. 2
Evidence Supporting PEG Superiority
The evidence base consistently demonstrates PEG's advantages across multiple outcomes:
Stool frequency: PEG increases bowel movements by approximately 2 additional stools per week compared to placebo, and 1-1.65 additional stools per week compared to lactulose. 3, 4
Symptom relief: PEG provides superior relief of abdominal pain and straining at stool compared to lactulose in both adult and pediatric populations. 3, 5
Stool consistency: PEG produces better stool form and consistency outcomes than lactulose. 3
Need for rescue therapy: Patients on PEG require fewer additional laxative products compared to those on lactulose. 3
Tolerability Profile
PEG demonstrates better overall tolerability than lactulose:
Reduced gas and bloating: Lactulose undergoes colonic fermentation producing gas, while PEG does not, resulting in significantly less flatulence with PEG. 5
Lower dropout rates: Clinical trials show better treatment adherence with PEG due to improved tolerability. 6, 4
Dose flexibility: PEG typically requires lower doses (1.6 sachets/day) compared to lactulose (2.1 sachets/day) for equivalent efficacy. 5
Practical Implementation
Starting dose: Initiate PEG at 17g daily (one sachet), which can be titrated based on response. 2
Timing: PEG can be taken at any time of day, mixed with 4-8 ounces of water or other beverages. 6
Duration: PEG is safe and effective for both short-term and long-term use, with no loss of efficacy demonstrated in studies extending beyond 6 months. 6, 5
When Lactulose May Be Considered
Despite PEG's superiority, lactulose remains an option in specific circumstances:
Cost considerations: In settings where PEG is not covered by insurance or is cost-prohibitive, lactulose may be used as an alternative osmotic laxative. 1
Patient preference: Some patients may prefer lactulose despite its conditional recommendation, though this should be discussed in context of the evidence. 1
Hepatic encephalopathy: Lactulose has additional indications beyond constipation that may make it preferable in patients with liver disease (though this is outside the scope of functional constipation). 7
Common Pitfalls to Avoid
Do not use stimulant laxatives as first-line therapy: Bisacodyl and senna should be reserved for short-term use (≤4 weeks) or rescue therapy after failure of osmotic laxatives like PEG. 8, 2
Do not assume all osmotic laxatives are equivalent: The guideline explicitly differentiates between strong recommendations (PEG) and conditional recommendations (lactulose, magnesium oxide), reflecting meaningful differences in evidence quality and clinical outcomes. 1
Verify adequate fluid intake: PEG requires sufficient fluid intake to work effectively; ensure patients understand the importance of hydration. 8
Escalation Strategy if PEG Fails
If PEG monotherapy is inadequate after appropriate trial:
Add stimulant laxative: Bisacodyl 5-10mg daily or senna 8.6-17.2mg daily for short-term use or rescue therapy. 8, 2
Consider prescription secretagogues: Linaclotide (72-145μg daily), plecanatide, or lubiprostone (24μg twice daily) all carry strong recommendations as second-line agents. 8, 2
Consider prokinetic agent: Prucalopride (5-HT4 agonist) is strongly recommended as second-line therapy. 2