You are here
Long-Term Pain Reduction Delivered by Capsaicin Patch, Phase II Study
"The study demonstrates that long-term pain relief may be provided by a single application of high-concentration capsaicin patches," said Dr. Backonja. "Importantly, because the patch-based treatment is localized, the systemic side effects of traditional treatments may be avoided." Despite expected pain increases during the procedure due to the pungent nature of capsaicin, overall tolerability was good. Dr. Backonja said no safety concerns were identified. A plasma sample analysis of patients confirmed the lack of systemic capsaicin absorption.
Every year, nearly 1 million Americans get shingles, a condition caused by varicella-zoster virus, the virus that also causes chickenpox. The condition usually results in a rash, blistering and, in many cases, severe pain. Many patients continue to have severe pain even after the rash disappears. This condition is called postherpetic neuralgia. It often persists for many years. Most current pain treatments for this pain syndrome require multiple doses each day and can cause side effects such as fatigue, light-headedness, fluid retention, constipation or dry mouth.
Capsaicin's Pain Relief Impact
Capsaicin, the pungent ingredient in hot chili peppers, activates certain receptors expressed by nerve fibers that specialize in the detection of painful stimuli. It is believed that the topical application of high doses of capsaicin can cause these capsaicin-sensitive nerve fibers to stop functioning. To the extent that these capsaicin-sensitive nerve fibers are involved in pain transmission, topically applied capsaicin could bring about a reduction in pain. For this reason, low-concentration capsaicin creams have been used with varying success for the treatment of postherpetic neuralgia and other pains. However, usage of these creams has been limited by the pain and inconvenience caused by the requirement for prolonged application several times a day, for weeks. The study used high-concentration capsaicin patches in a single one-hour application and provided pain reduction for four weeks.
Single Application Treatment Delivers Pain Relief without Safety Problems
The Phase II study for what NeurogesX calls NGX-4010 was a double-blind, randomized controlled, multi-center study evaluating the tolerability, safety, and efficacy of high-concentration capsaicin patches in the treatment of postherpetic neuralgia. Forty-four patients at nine centers in the United States were given a single treatment and then followed for four weeks.
The treatment procedure consisted of a single application of a topical non-prescription anesthetic for one hour, followed by a one-hour patch application on the most painful area, up to a maximum of 1000 cm(2). The control group received a low-concentration capsaicin patch.
Patients recorded their pain intensity twice daily on an 11-point numerical scale. The primary efficacy endpoint was the change from baseline in morning/evening average pain (days 8-28).
In yesterday's "Late Breaking Science" session, Dr. Backonja discussed the study results in an oral presentation.
Forty-two percent of patients in the active group experienced a pain decrease of 33 percent or more, compared to 8 percent in the control group. Pain decreases in the active group were noted on the first day after the procedure and remained stable throughout the four-week observation period.
"As a purely local treatment without the potential for systemic side effects, high-concentration capsaicin patches could be a very effective and safe treatment alternative for patients suffering from postherpetic neuralgia," said Thorsten von Stein, M.D., Ph.D., vice president of clinical development at NeurogesX, Inc., the company that sponsored the multi-center study.
Further Studies in Pain Treatment
NeurogesX said it will begin pivotal studies of NGX-4010 in April 2003. The company is also in the process of developing additional medicines for other pain syndromes, including the pain caused by tissue injury.