Chronic constipation is characterized by problems with bowel movements that last for at least 12 weeks. Problems include passing fewer than three bowel movements a week, straining during bowel movements, and lumpy or hard stool. If other gastrointestinal symptoms are present, such as bloating and abdominal pain, the constipation may be part of irritable bowel syndrome (IBS).

The management of constipation often begins with changes in diet (e.g. increase fluid intake), and behavior (e.g. use the bathroom at a specific time). Patients who do not respond to these changes are usually offered fiber supplements and simple laxatives. If the constipation persists and a specific cause cannot be found, many different drug options are available. However, despite constipation being a common problem, for which multiple drugs have been available for many years, the evidence for such treatments is largely missing.

The "Drug Class Review on Constipation Drugs" compares the safety and effectiveness of seven drugs used to treat chronic constipation in adults and children. A summary of the findings is below.

How do the drugs used to treat chronic constipation and irritable bowel syndrome with predominant constipation compare?

In adults, polyethylene glycol has been shown to be effective in the treatment of chronic constipation. Less evidence supports the efficacy of psyllium. The strongest evidence is for Tegaserod which has shown to be effective in not only chronic constipation in adults, but also constipation associated with irritable bowel syndrome in both adults and children. However, because of safety concerns, tegaserod is currently not available in the US. The evidence on lubiprostone has been published as abstracts only.

There is no evidence on the efficacy of docusate calcium, docusate sodium, and lactulose in treating chronic constipation in adults, and currently there are no studies on the general efficacy for the treatment of chronic constipation in children.

The evidence comparing the efficacy of two drugs is sparse and fraught with methodological limitations. Results indicate that polyethylene glycol is more effective than lactulose in adults and children and more than psyllium in adults. Docusate sodium had efficacy similar to psyllium in adult patients.

No studies exist on the efficacy of docusate calcium, docusate sodium, lactulose, polyethylene glycol, and psyllium for the treatment of irritable bowel syndrome. [full review]

Does treatment duration influence the effectiveness of drugs used to treat chronic constipation?

Currently there is not enough evidence to determine whether the duration of treatment influences the effectiveness of treatment, or at which point a treatment should be changed in a patient not responding to a drug.

Studies lasted from 2 to 12 weeks, the effectiveness of treatments was similar between the shorter and longer trials, and none of the trials addressed the question of when to switch therapies in non-responders. [full review]

How do the drugs used to treat chronic constipation compare in terms of safety?

Overall, the quality of the evidence is poor and available for only a few of the drugs reviewed, and should be interpreted with caution.

In adults with chronic constipation, or chronic constipation associated with irritable bowel syndrome, both polyethylene glycol and psyllium were well tolerated with no significant difference in adverse events. When both drugs were compared to lactulose, polyethylene glycol had lower rates of flatus and abdominal pain but higher rates of diarrhea, whereas psyllium had lower rates of diarrhea but was less palatable.

Polyethylene glycol was reported to be well tolerated in children, the most common side effect being diarrhea. There is mixed evidence about differences of adverse events between lactulose and polyethylene glycol, but none of the events were severe. [full review]

Does age or ethnicity influence the safety of the drugs used to treat chronic constipation?

Evidence is either limited (lubiprostone) or unavailable (docusate calcium, docusate sodium, lactulose, lubiprostone, polyethylene glycol, psyllium or tegaserod) on whether gender, age, ethnicity or co-mordities influences the safety and efficacy of these drugs. [full review]

Drugs included in this review

*Tegaserod was taken off the market in March 2007 because of an increased risk of cardiovascular events.

Further information

This PubMed Clinical Q&A was reviewed by Gerald Gartlehner, MD, MPH.

For the full report and evidence tables, please see:
Gartlehner G, Jonas DE, Morgan LC, et al. Drug Class Review: Constipation Drugs: Final Report [Internet]. Portland (OR): Oregon Health & Science University; 2007 Sep. Available at: http://www.ncbi.nlm.nih.gov/books/NBK10503/.