April 3, 2003 (Honolulu) -- A one-hour application of a patch containing the pungent chili pepper ingredient capsaicin reduced pain for a month in patients suffering from postherpetic neuralgia, a preliminary study shows.
Relatively low doses of capsaicin cream have been used for these patients for many years. This was the first study to suggest a high-dose patch could result in pain relief for one month with a single one-hour application of the patch.
Postherpetic neuralgia is the pain that persists following nerve damage caused by infection of the varicella zoster virus. The infection, called shingles, causes a painful rash. The rash resolves, but nerve damage and pain persist as postherpetic neuralgia. The pain can last for months or years.
In the study, presented at the annual conference of the American Academy of Neurology, the one-hour pain relief patch reduced pain by 33% for up to one month in 42% of patients receiving high doses of the drug, compared with a placebo patch.
Misha-Miraslav Backonja, MD, neurologist at the University of Wisconsin, Madison, who presented the results, says 44 patients were involved in the trial at nine centers in the United States. Twenty-six patients received a high concentration capsaicin patch.
The patients had suffered from chronic pain an average of three years, but some of the patients reported chronic pain for up to 13 years, Backonja says. They had been taking antidepressant medication, tricyclic antidepressants, anti-epileptic medications, or opioid analgesics.
"They were taking medication, but that was not enough," he tells WebMD.
Backonja says patients were first treated for one hour by a local anesthetic to prepare for the placement of the patch. The patches were placed on the most painful spot, but not on the face.
Capsaicin activates certain receptors in nerves of the skin, causing burning sensations followed by inactivation of those receptors, numbing the nerves to further pain.
Kenneth Nakano, a Waikiki, Hawaii, neurologist who co-chaired the session, tells WebMD in a phone interview that some listeners at the presentation had a healthy dose of skepticism about the results.
"There may be some basis for it (the patch), but some will be skeptical," Nakano says. Still, he says, "It's intriguing," and warrants further study.
Norman Latov, MD, medical and scientific director of The Neuropathy Association in New York City and professor of neurology at Cornell University, tells WebMD in a phone interview that the pain reduction may have been caused because nerves were essentially dead where the patch was in contact with the skin.
Latov says the pain from postherpetic neuralgia can range from annoying to overwhelming. He says he anticipates increases in the number of cases as the population ages and becomes more vulnerable to an outbreak of varicella zoster.
The study was supported by NeurogesX Inc.