Polyethylene glycol (PEG) 3350, a non-absorbable, nonmetabolized osmotic agent, is employed in lavage solutions for gut cleansing. The present study compared the efficacy of PEG and lactulose in chronic constipation. 

The study included a total of 115 patients with chronic constipation and administered them initially two sachets containing either PEG (13 g/sachet) or lactulose (10 g/sachet) and rendered them an option to change the dose to one or three sachets/ day, depending on response. 

The study found-

• Ninety-nine patients completed the trial.
• After four weeks, a higher number of stools and a lower median daily score for straining at stool in patients in the PEG group (n=50) than in patients in the lactulose group (n=49).
• Greater overall improvement in the PEG group.
• Similar clinical tolerance in the two groups but less frequent flatus in the PEG group.
• A higher mean number of liquid stools in the PEG group, but a significant difference only for the first two weeks.
• No serious adverse events and no significant change in laboratory tests in either group.
• At the end of the study, patients in the PEG group used 1.6 (0.7) sachets per day, and those in the lactulose group used 2.1 (0.7) sachets per day.
• Sixty-one patients completed a further two months open study of one to three sachets PEG/day; with no loss of efficacy and no serious toxicity. 

This study shows that Low dose PEG 3350 is more effective than lactulose and is better tolerated.

Attar A, Lemann M, Ferguson A, et al. Comparison of a low dose polyethylene glycol electrolyte solution with lactulose for treatment of chronic constipation. Br J Surg. 2010 Nov;97(11):1603-13. Doi: 10.1002/bjs.7212