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Antidepressant May Relieve Neuropathic Pain

Wellbutrin may have milder side effects than older medications

MONDAY, Nov. 12, 2001 (HealthDayNews) -- A new-generation antidepressant with milder side effects than existing treatments may help Americans suffering from neuropathic pain, suggests a new study.

Neuropathic pain, which results from some type of nerve dysfunction, causes burning, tingling or shooting sensations. "It's a central nervous system problem that involves hyperexcited nerves," says Krista Brecht, a clinical nurse specialist in acute and chronic pain management at McGill University in Montreal.

A simple light touch, even contact with clothing, can trigger pain. People with the disorder also are extremely sensitive to stimuli that normally cause pain, experts say.

The condition, thought to affect at least 1.7 million Americans, can originate in either peripheral nerves or in the brain, depending on the type of condition. People who've had strokes can develop something called post-stroke pain, which originates in the brain, while people with diabetic neuropathy have a problem with nerves elsewhere in the body.

As many as 80 percent of people with neuropathic pain have been treated with tricyclic antidepressants (TCAs), Brecht says. "It's still a very effective first-line treatment modality," she says.

If TCAs don't work, doctors often turn to drugs that originally were developed as anticonvulsant medications, including Neurontin (gabapentin) and Tegretol (carbamazepine).

But now, a report in the Nov. 13 journal Neurology says bupropion SR, which is sold as Wellbutrin SR, provides significant relief to patients with this often debilitating condition.

Lead author Marilyn Semenchuk conducted the research while working at the University of Arizona at Tucson. Her research on bupropion SR, was partially funded by GlaxoSmithKline of Research Triangle Park, N.C., which makes bupropion, and led to her current employment with the company, where she now is a central nervous system regional medical scientist.

"[TCAs] had been the gold standard for many years for treating pain until we had some of the newer drugs, in particular Neurontin," Semenchuk says. But while effective, she says TCAs aren't perfect, and "many patients can't tolerate them because of the side effects."

"They typically have a higher incidence of side effects associated with their use," she says, citing dry mouth, blurred vision, constipation and effect on cardiovascular function as possibilities.

Semenchuk says she wanted to study bupropion SR because preliminary studies suggested it targets the same neurotransmitters but without the side effects of the older antidepressants.

The researchers enrolled 41 men and women, ages 23 to 88, who had been diagnosed with neuropathic pain. Testing ruled out depression in each patient to ensure that any effect from the treatment was due to pain relief and not relief of depression, the researchers say.

For one week, half the participants received 150 milligrams of bupropion SR; that was increased to 300 milligrams for the next five weeks. The other group received similar doses of a placebo. Then for the next six weeks, the group that had been taking the actual drug received a placebo, and the placebo group took bupropion SR. None of the participants knew whether they were receiving the drug or the placebo.

Using a standardized pain-scoring method, the researchers found that 73 percent of participants said their pain was "improved" or "much improved" during the six weeks they took bupropion SR. One person with trigeminal neuralgia -- a nerve disorder characterized by pain in the lips, gums, cheek or chin -- reported complete pain relief while on the drug.

However, 90 percent of the participants said their pain was unchanged or worse during the six weeks they took the placebo.

"When they got the active drug, there was clearly a big difference in terms of their pain symptoms versus when they got the placebo," Semenchuk says.

People receiving the drug did report some side effects, including dry mouth, problems sleeping, headache and gastrointestinal upset, the researchers say. Most people rated the symptoms as mild, although two participants dropped out of the study early, one because of nausea and vomiting while on both the drug and the placebo, and one because of dizziness while on the drug.

The sustained-release action of the drug may produce fewer side effects, Semenchuk says. "Plus, when you have sustained release, you only have to take the medication twice a day," she says. The immediate-release version must be taken three times day.

"It's hard enough having a pain condition that impairs your quality of life. You certainly don't need to be adding medications that are going to have a negative impact on quality of life," she says.

"It gives physicians another potential agent to help benefit patients," she says. However, she says larger studies are needed, and people with a history of a seizure disorder can't take bupropion SR.

She says neuropathic pain can have a variety of origins, making it less likely that any drug will be a magic bullet that helps all patients. "So far, based on all the clinical research that we've done to date in neuropathic pain, we've yet to find one drug that will completely eliminate a patient's pain," she says.

Rather, she suspects that combinations of drugs will provide the best pain treatment.

What To Do

To find out more about neuropathic pain, go to the Society for Neuroscience online, take a look at an article from Hospital Practice or go to the HelpForPain Web site.

For more on bupropion SR, visit GlaxoSmithKline online.

SOURCES: Interviews with Marilyn R. Semenchuk, Pharm.D., central nervous system regional medical scientist, GlaxoSmithKline, Research Triangle Park, N.C.; Krista Brecht, R.N., M.S.C.N., clinical nurse specialist in acute and chronic pain management, department of anesthesia, McGill University, Montreal; Nov. 13, 2001 Neurology
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