PEG vs Lactulose for Constipation

Introduction to Constipation Treatment

The American Gastroenterological Association-American College of Gastroenterology recommends using polyethylene glycol (PEG) preferentially over lactulose for the treatment of chronic constipation in both adults and children, with a strong recommendation and moderate certainty of evidence for PEG 1, 2

The American Gastroenterological Association-American College of Gastroenterology provides a strong recommendation with moderate certainty of evidence for PEG, while lactulose receives only a conditional recommendation with very low certainty of evidence 3, 4

PEG demonstrates superior efficacy across multiple outcomes, including stool frequency, with an increase of 2.90 complete spontaneous bowel movements (CSBMs) per week and 2.30 spontaneous bowel movements (SBMs) per week compared to placebo, with durable response over 6 months 4, 5
PEG achieves a 3.13-fold higher responder rate compared to placebo, with 312 more responders per 1,000 patients 5
PEG provides better global symptom relief, with 454 more per 1,000 achieving relief, and improvements in stool form and straining compared to lactulose 1, 2

Common PEG side effects, such as abdominal distension, loose stool, flatulence, and nausea, are generally mild to moderate and dose-dependent 2, 4
Lactulose's major limitation is bloating and flatulence, which are dose-dependent and common, and may significantly limit its use in clinical practice 3

The standard dose of PEG is 17 g daily mixed in 8 ounces of liquid, and can be titrated from 1-3 doses daily based on response 4, 5
The American Gastroenterological Association-American College of Gastroenterology recommends starting with PEG 17 g daily as first-line therapy, with lactulose reserved for PEG failures 3, 4

The treatment algorithm recommends starting with PEG 17 g daily, with titration based on response over 2-4 weeks, and considering lactulose only if the patient fails or is intolerant to PEG 3, 4, 6

PEG offers an efficacious and tolerable solution with a good safety profile for elderly patients, particularly those with cardiac or renal comorbidities 7

PEG is widely available over-the-counter without prescription and is relatively inexpensive, despite being more costly than lactulose, with its superior efficacy and tolerability justifying any modest cost difference 2, 4, 6

The evidence clearly supports PEG as first-line therapy, and lactulose should be reserved for PEG failures, with adequate hydration and proper dosing of PEG being crucial for effective treatment 3, 4, 8

The primary disadvantages of PEG include gastrointestinal side effects such as diarrhea, abdominal distension, flatulence, and nausea, though these are generally mild to moderate and dose-dependent 9
Diarrhea is the most significant adverse effect, occurring 158 more per 1,000 patients compared to placebo, though most cases are mild to moderate 9
Abdominal distension and bloating can occur, particularly when initiating therapy or with higher doses 9, 10
Nausea may develop in some patients 9
Requires adequate fluid intake to work effectively - insufficient liquid volume (less than 8 ounces per dose) can lead to treatment failure 9
Volume burden may be problematic for some patients who must mix 17g in 8 ounces of liquid daily 9
Serious adverse events were very rare in trials, with confidence intervals too wide to draw definitive conclusions about risk (RR 0.47, CI 0.16–1.33) 9

Excessive gas production results from bacterial fermentation of the unabsorbed disaccharide in the colon 10
Lower overall patient satisfaction and global symptom relief compared to PEG 9