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Cancer Pain Remedy Wins Orphan Drug Status

Cancer Pain Remedy Wins Orphan Drug Status

The FDA has granted orphan drug status to methylnaltrexone, a medication that blocks the side effects of morphine without interfering with pain relief.

The "orphan" designation provides special tax and other potential benefits to sponsors for research attempting to develop drugs to treat rare diseases. It is designed to encourage research and testing of drugs that may be clinically useful but are not likely to attract the interest of pharmaceutical companies because the costs of development and distribution may exceed anticipated revenues from sales.

"Orphan drug status is a big step toward bringing this important drug to a population of patients in need," said Michael Roizen, md, professor and chairman of the department of anesthesia and critical care at the University of Chicago. Roizen and colleague Joseph Foss, md, assistant professor of anesthesia and critical care, have done the preliminary animal and clinical testing of the drug.

UR Labs, a privately held corporation active in drug development, has been working with the University of Chicago to develop methylnaltrexone for use in patients with cancer pain. United States and international patents have been filed for many indications.

Many patients with chronic pain cannot tolerate the side effects of long-term use of opioid-based pain medications such as morphine. These side effects include nausea and severe constipation. As many as 40% of chronic pain patients chose to live with the pain rather than endure the side effects.

But methylnaltrexone may make morphine more manageable. Recently published studies from Roizen, Foss and colleagues Chun-Su Yuan and Jonathan Moss, also from the University of Chicago, demonstrated that methylnaltrexone can block the side effects of opioid-based pain relievers, preventing the constipation without altering its effects on pain.

New Drug Doesn't Cross Blood-Brain Barrier

Methylnaltrexone was invented by the late University of Chicago pharmacologist Leon Goldberg, md, phd, to help a friend suffering from cancer. He started with naltrexone (Trexan), an established antiaddiction drug that blocks the effects of morphine.

Goldberg altered the drug slightly so that it continued to block the effects of morphine throughout the body, preventing the nausea and constipation caused by morphine. But by attaching a methyl group to the naltrexone, he altered the molecule to prevent it from crossing the blood-brain barrier. As a result, it did not interfere with morphine's effect on pain, which is centered in the brain.

Despite encouraging results in animal models and early trials in human volunteers, no pharmaceutical company has yet been willing to make a long-term commitment to developing methylnaltrexone.

"The costs of developing a new drug can be astronomical," said Roizen. "For a medication targeted to only a small group of users, fewer than 200,000 people, it can be difficult for the manufacturer to recoup that investment. Orphan-drug status radically improves the odds of bringing such drugs into use."

Phase II-III trials of methylnaltrexone, which test how well the drug works and how it compares to alternative medications, will begin at the University of Chicago Hospitals Clinical Research Center and a hospice in Great Britain this year.

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