Polyethelyne Glycol vs. Lactulose

Which relieves chronic constipation more effectively?

Chronic constipation is a disorder in which an individual experiences lumpy or hard stools that are difficult to pass. It affects 15-30% of Canadians, and is more common in children, the elderly, and women. Many treatments are available to increase elimination frequency and soften stools, including fibre, stool softeners, laxatives, and enemas, all with differing degrees of success.

One type of laxative, osmotic, works by drawing water into the large bowel (colon) from the surrounding tissue, thereby increasing fluid content and softening fecal matter, allowing the person to have more frequent and comfortable bowel movements. These laxatives are very effective; however, speak with your physician before using them long-term in order to avoid any negative side effects, such as electrolyte imbalance. There are four main subgroups of osmotic laxatives: saline, lactulose, polymer, and glycerine. In this article, we will focus on two laxatives: lactulose and polymer.

Lactulose (e.g., Duphalac®) is a synthetic, non-digestable, sugar-like agent (not to be confused with lactose, the sugar found in milk) that helps to empty the bowel at a slow rate, taking 6 hours to 2 days to take effect. PEG (e.g., PegaLAX®) is a polymer compound that consists of large molecules that help retain water in the stool, and it usually works within 6 hours.

A meta-analysis recently published in The Cochrane Database of Systematic Reviews1 compared the results of 10 separate studies that looked at the management of chronic constipation to see if one of these laxatives is more effective.

Together, the ten trials covered results from 6 different countries between 1997 and 2007, with 868 participants aged 3 months to 70 years. The results were strong and showed that PEG is more effective than lactulose in treating chronic constipation. Of the trials conducted, five reported weekly stool frequency; in each of those studies, PEG resulted in an increased stool frequency over lactulose.

PEG also had a higher score than lactulose on the Bristol Stool Chart – which measures the softness of stools – in the two studies that used this measurement. Three trials compared relief of abdominal pain; in two of them, PEG came out on top and in the third, PEG and lactulose were equally effective. Three trials also showed that individuals using PEG needed fewer additional products to relieve constipation than those taking lactulose.

Overall, the meta-analysis found polyethylene glycol to be more effective than lactulose at increasing stool frequency, relieving pain, and reducing the need for additional products in both adults and children. Therefore, the researchers contend that polyethylene glycol should be preferred over lactulose when treating chronic constipation.

First published in the Inside Tract® newsletter issue 177 – 2011
1. Lee-Robichaud H et al. Lactulose versus Polyethylene Glycol for Chronic Constipation (Review). Cochrane Database of Systematic Reviews. 2010;7. Available at http://www2.cochrane.org/reviews/en/ab007570.html. Accessed 2011-01-24.