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Capsaicin Patch Eases Shingles Pain

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MADISON - The chronic pain left behind by shingles causes intense misery, so it sounds a bit like torture to treat it with a high dose of the chemical responsible for the heat in hot peppers.

But a clinical trial of a high-dose capsaicin patch, done at the University of Wisconsin School of Medicine and Public Health (SMPH) and other institutions, shows that it is surprisingly effective on the vexing problem known as post-herpetic neuralgia (PHN). In recent tests of an 8 percent capsaicin dermal patch, about 40 percent of the people had pain relief lasting as long as 12 weeks.

Results were published in the December edition of The Lancet-Neurology.

"We were surprised at the long-term pain relief," said Dr. Miroslav Backonja, a professor of neurology at SMPH and the study' lead author. "People had pain relief for up to 12 weeks from a patch that was applied for an hour."

The study of 402 PHN sufferers at 55 research centers in the United States was financed by NeurogesX, a California company that is hoping for FDA approval of the high-dose capsaicin patch.

Post-herpetic neuralgia results when the herpes zoster virus, which also causes chickenpox, becomes active again, after living dormant in the nerve roots. A painful skin rash breaks out along the nerve, usually on the head and face or trunk. The virus damages nerves in the area of a shingles outbreak, causing an intense pain that can last for months after the rash disappears.

Backonja, also a practicing UW Health neurologist, said PHN is most common in older people. While shingles tend to go away completely in younger patients, Backonja said that more than 40 percent of people older than 65 years who have an episode of shingles will develop PHN.

"This is a problem that plagues the elderly, and this is becoming a health care problem because that is the most rapidly growing segment of the population," he said.

Sufferers describe the pain as burning and itching. In an extreme case reported in literature, a patient had scratched through her skull all the way into her brain. Backonja took care of a patient who had to quit her job because PHN on her back made her skin so sensitive she couldn’t wear any clothing.

Still, he was concerned that no one would want to participate in the trial because of the strength of the capsaicin. Topical capsaicin cream, which is sold over the counter as a remedy for arthritis pain, contains concentrations of 0.025 percent to 0.075 percent, so the 8 percent concentration is more than a hundred times as strong.

"My first concern was that nobody would be able to tolerate it but I was flabbergasted how well they did tolerate it," Backonja said.

Patients had their skin numbed with topical lidocaine cream before the patch was applied. Some were also given oral pain medicine for the pain caused by treatment. About half the patients were assigned to a control group, and received a patch with the low dose of capsaicin similar to the over-the-counter cream. Backonja said it was necessary to have some capsaicin in the control patch, because it causes obvious reddening of the skin, and patients who didn’t have reddened skin would then know they had received the control patch.
 
About 40 percent of patients treated with the high-dose patch reported a drop in pain, with an average decrease in pain of about 30 percent, as measured on the 1 to 10 on the numeric pain rating scale. In contrast, about 30 percent of the control group experienced a decrease in pain, but their reported pain decrease was smaller.
 
Backonja said capsaicin may work by "pruning back" damaged endings of nerve cells.

"What we think happens is that the virus damages the nerve endings, and these damaged nerve endings are like live wires," Backonja said. "If you ‘prune them back’, they stop short-circuiting."

Capsaicin is known to use the same pathways the nerves use to conduct the sense of heat, which is probably why spicy salsa makes you feel warm all over.

Backonja said he once had a patient who discovered that eating enough hot salsa helped ease his minor but still bothersome attacks of PHN pain, which would come in waves. But he sees promise in the capsaicin patch for more chronic cases.

"It has the advantage of being a topical treatment," he said. "Many of these patients are on multiple medications, and the advantage of the patch is that you don’t have to worry about drug interactions."

This is a stage three clinical trial for the NGX-4010 patch, meaning that it could be approved soon for clinical use. The NeurogesX company says it expects European Union approval in early 2009, and that the FDA will begin reviewing the drug for U.S. approval late in 2009.
 

Date Published: 04/30/2009

News tag(s):  research

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