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| |  Capsaicin Patch Fails to Ease HIV-Associated Polyneuropathy: Presented at CROI By Ed Susman SAN FRANCISCO -- February 21, 2010 -- The capsaicin patch -- approved for easing shingles pain -- failed to reduce discomfort any more than placebo for individuals suffering from HIV-associated distal sensory polyneuropathy, according to a study presented here at the 17th Conference on Retroviruses and Opportunistic Infections (CROI). During a poster presentation on February 18, researchers said that treatment with the patch reduced pain scores by 29.5%, but a placebo patch treated with a tiny concentration of capsaicin to mask randomisation in the double-blind trial reduced pain scores by 24.6% -- a nonsignificant difference (P = .10). This unexpectedly potent placebo response ended any chance that the patch could be effective for the HIV polyneuropathy indication, according David Clifford, MD, Washington University, St. Louis, Missouri. He called the findings disappointing given the promising phase 2 results. Capsaicin, the active ingredient that gives cayenne pepper its burn, acts on receptors in nociceptive nerve fibres. Prolonged exposure can actually obliterate these sensory axons, blocking pain signal transmission. Because the receptors take a few months to regenerate, this mechanism is assumed to be the reason the skin patch, with its 8% concentration of capsaicin, works against neuropathic pain, explained Dr. Clifford. For the study, the researchers randomised patients with HIV-associated distal sensory polyneuropathy to receive the active capsaicin patch (n = 332) or a placebo patch (n = 162) that consisted of a 0.04% solution of capsaicin. The patients were questioned about pain relief from polyneuropathy after 30 minutes of patch application and after 60 minutes. The patch was wrapped around the entire painful area for patients in both groups. All groups received a 60-minute application of 4% lidocaine cream immediately before treatment. For the 30-minute application comparisons, the 8% capsaicin treatment tended to reduce pain score more than the 0.04% capsaicin control (-26.1% vs -19.1%; P = .1032). For the 60-minute application comparisons, the full-strength patch was no better than its control (-32.8% vs -30.1% pain score change; P = .5125). Most patients tolerated capsaicin treatment well, with 97% completing at least 90% of intended patch duration, the investigators noted. Dr. Clifford said that HIV-associated distal sensory polyneuropathy remains a condition without an approved treatment. Funding for this study was provided by NeurogesX, Inc. [Presentation title: A Multicenter, Randomized, Double-Blind, Controlled Study of NGX-4010, a High-Concentration Capsaicin Patch, for the Treatment of Painful HIV-Associated Distal Sensory Polyneuropathy. Abstract 411]
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