When ordinary over-the-counter laxatives fail to work, doctors turn to other medications to treat people with constipation. Now, a new review of existing research finds that one common drug treatment is better than another is at helping patients who are desperate to get things moving.
The Cochrane Library reviewers report that the drug polyethylene glycol “works a bit better” than lactulose, said Dr. Richard L. Nelson, a surgeon at Northern General Hospital in Sheffield, England. That is good news for patients: polyethylene glycol is now available without a prescription.
In many patients, constipation is not just a matter of not eating enough fiber. In some cases, they suffer from a backed-up digestive tract as a side effect of disease, pregnancy or medications.
In other cases, the nerves in the gut fail to function properly. Essentially, “the colon becomes lazy,” said gastroenterologist Dr. Satish Rao, a professor of medicine at the University of Iowa.
There is a variety of laxatives available in drugstores, including milk of magnesia, fiber supplements and stool softeners. Of course, there are also the old standbys like bran muffins and prune juice.
If those do not work, doctors often turn to lactulose, which only is available by prescription, and polyethylene glycol, which recently became an over-the-counter medication under the brand name MiraLax.
Both drugs draw fluid into the intestines, making it easier for people to defecate.
In the new review, researchers performed a meta-analysis by combining the results of 10 controlled and randomized studies into the two drugs.
The review was published by The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.
The studies, published between 1997 and 2007, examined the experiences of 868 people -- 322 adults and 546 children. Researchers assigned participants randomly to undergo treatment with lactulose or polyethylene glycol.
Six of the studies did not say where they received funding; drug companies funded three.
The researchers found that polyethylene glycol was better than lactulose in several areas, including the number of stools per week and the form of the stool. Those who took polyethylene glycol also had less need for other medications to treat their constipation.
Children who took polyethylene glycol had less abdominal pain, but there was not a difference in adults between the two drugs.
The two drugs are “supposed to have no side effects,” Nelson said, and indeed, they do not harm the colon over the long term like some other laxatives. However, the review points out that both drugs can cause diarrhea, while polyethylene glycol can cause nausea and pain while lactulose can lead to bloating and flatulence.
Lactulose can cause those problems, said gastroenterologist Rao, who is familiar with the review findings. “It’s slow in its action and really doesn’t work very well except in the elderly group.”
Rao said he prescribes polyethylene glycol regularly and rarely recommends lactulose to patients.
Lactulose appears to be more expensive. As of December 2008, Consumer Reports reported that, depending on the dose, the monthly cost of lactulose ranged from $40 to $82 and polyethylene glycol from $23 to $39.
There are other factors to consider. Rao said patients would prefer to take a pill for long-term aid, but both drugs are available only as liquids. “Neither of these compounds would work best for them,” he said.
Nelson, the review co-author, also said the drugs are not appropriate in every case of constipation. They are not appropriate in the case of an obstruction in the intestines, nor are they ideal when a fiber supplement would be sufficient.
He does not recommend them when constipation only happens on occasion and is not a “major complaint.”
Some people swear by specific cycles of regularity: they like to go when the clock (or the calendar) suggests they should and feel out of whack when they do not. Still, the fact is that “bowel habits vary,” Nelson said. “The border between normal variation and a symptom of disease can be very hazy.”
In other words: one patient might go often and another might not, and both might be perfectly normal. Alternatively, the second patient might need one of these drugs.
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Lee-Robichaud H, et al. Lactulose versus polyethylene glycol for chronic constipation. Cochrane Database of Systematic Reviews 2010, Issue 7.