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Drugs Ease Hard-to-Treat Constipation

Results of Resolor Study Are Positive; Relistor Helps Opioid Constipation

Constipation Help for Pain Sufferers

Opioid drugs are a huge boon in offering pain relief to patients with severe pain. But they cause their own form of suffering -- constipation that often cannot be relieved by laxatives. This problem often means patients have to cut back on opioid use, sometimes with a terrible increase in pain.

The drug naltrexone blocks opioid drugs from attaching to receptors, thus blocking their painkilling effects. Relistor is a form of naltrexone that has limited ability to enter the brain. The idea is to block the unwanted side effects of opioids, such as constipation, without blocking their painkilling effects.

In a clinical trial supported by Progenics, which is developing Relistor in collaboration with Wyeth, 133 patients with advanced illness and terminal disease who had been on opioids for two or more weeks received under-the-skin injections of Relistor or an inactive placebo.

Nearly half the Relistor-treated patients had a bowel movement within four hours of the first dose, compared with 15% of the placebo group. Time to bowel movement was significantly shorter for Relistor patients than placebo patients.

Importantly, none of the patients showed signs of opioid withdrawal or had changes in their pain scores.

Relistor "may represent an important therapeutic option for patients with advanced illness who are suffering from opioid-induced constipation," conclude Jay Thomas, MD, PhD, of San Diego Hospice and the Institute for Palliative Medicine, San Diego, and colleagues.

In an editorial accompanying the Thomas report in the May 29 issue of The New England Journal of Medicine, Harvard researchers Charles Berde, MD, PhD, and Samuel Nurko, MD, MPH, commend the Thomas team on its work.

However, Berde and Nurko wonder why only half of patients responded. Their hypothesis is that the constipating effects of opioids stem not only from opioid action in the gut, but also in the brain, which Relistor cannot reach.

"Future studies in a larger number of patients may help to delineate predictors of the success or failure of [Relistor] in specific subgroups of patients, and may guide decisions about increasing or decreasing the dose for various patients," they suggest.

Relistor was approved by the FDA in April 2008 for the treatment of opioid-induced constipation in patients with late-stage, advanced illness who are receiving opioids on a continuous basis to help alleviate their pain.

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