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Topical Capsaicin Confers Moderate to Poor Pain Reduction for Neuropathic and Musculoskeletal Disorders

Topical capsaicin offers moderate to poor efficacy for pain caused by neuropathic and musculoskeletal disorders, but is more effective than is placebo, according to the findings of a meta-analysis of studies in adults with chronic pain.

With 8 weeks of topical .075% capsaicin, "for around every six patients, one would achieve at least a 50% reduction in pain who would not have done so if given placebo," writes R. Andrew Moore, director of research, and colleagues at University of Oxford, United Kingdom.

In a search of randomised, active or placebo controlled trials of capsaicin in adults with neuropathic disorders such as diabetic neuropathy, postherpetic neuralgia, polyneuropathy, other neuropathies, or chronic postoperative pain; or musculoskeletal problems from arthritic disorders, back pain, fibromyalgia, or other chronic muscle pain, the investigators identified 16 papers including a total of 1,556 patients, aged from 20 to 95 years.

Overall, .075% capsaicin resulted in a 50% reduction of pain at 4 weeks for a mean of 57% of patients compared with a response of 42% in patients using placebo for neuropathic conditions. Mean response at 8 weeks was 60% in the capsaicin patients and 42% among those using placebo. Both treatment durations had a relative benefit of 1.4.

For patients with musculoskeletal conditions, the mean response at 4 weeks was 38% for .025% capsaicin or plaster compared with 25% for placebo, for a relative benefit of 1.5.

While capsaicin showed lesser overall efficacy for musculoskeletal conditions, the difference was not statistically significant from neuropathic conditions, and the authors note the availability of too few trials to determine if the difference was due to a lower capsaicin dose.

Local adverse events occurred in 54% of patients using capsaicin and resulted in a 13% withdrawal rate compared with 15% and 3%, respectively, in the placebo groups, overall.

"Most of the trials stated that patients had moderate or severe chronic pain," the authors note, "and some recruited patients only if they were unresponsive to other treatments." "For patients with chronic moderate or severe pain," the authors suggest, "even a small reduction in pain can be beneficial."

BMJ doi:10.1136/bmj.38042.506748.EE (published 19 March 2004).

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