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New Drug Relieves Troubling Side Effect of Cancer Painkillers

WebMD Health News
Reviewed by Gary D. Vogin, MD

Oct. 31, 2001 -- Pain relievers for people with cancer often cause constipation. But researchers have discovered a way to get around this disturbing side effect.

Jonathan Moss, MD, PhD, presented his evidence supporting the new drug at a meeting sponsored by the American Medical Association. The drug, methylnaltrexone, is able to block the action of opioids on the bowels.

While opioids, like morphine, stop pain by blocking the pain-sensing pathways in the body, they also affect the gut and stop the bowels from moving. Methylnaltrexone allows morphine to relieve pain but blocks its action on the bowels.

In a news release, Moss says this is the first medication that reverses constipation caused by morphine and other opioids without interfering with the pain-relieving effects.

Moss is a developer of methylnaltrexone and serves as a consultant to Progenics Pharmaceuticals, which has purchased the rights to the drug.

Moss and his colleagues tested the drug in heroin addicts, since the FDA was unwilling to risk interfering with pain relief in people with cancer. The researchers looked at addicts on methadone, which is also an opioid like mophine and likewise also causes constipation.

Among 22 methadone users, 21 of them had immediate bowel movements after taking methylnaltrexone. And none of them experienced withdrawal symptoms -- a sign that the drug would not interfere with the pain-relieving effects of opioids.

"The drug clearly works," says Moss. "If there were any evidence methylnaltrexone was blocking pain relief, these patients would have suffered some drug withdrawal symptoms.

"I am hopeful that it will [only] take two to three years to complete clinical trials necessary to earn FDA approval, after which these problems will be nonevents. Our experience in almost 400 people to date suggests that the drug is safe and effective ..." says Moss.

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