Thursday, October 22, 2009

Chile Peppers Aid Neuropathic Pain – Somewhat

For patients with peripheral neuropathy, a new research review suggests that up to 4 of 10 sufferers could experience some pain relief from the active component of chili peppers — topical capsaicin cream. Peripheral neuropathies include nerve disorders that can cause burning pain, tingling, numbness, weakness, and other discomforts. However, there are some strong limitations of the research.

Oxford University researchers Sheena Derry and Andrew Moore led the Cochrane Collaboration systematic research review, which included 8 randomized, double blind, placebo-controlled trials involving more than 1,000 adult participants. The capsaicin formulations investigated were either mild creams that patients can apply themselves or a newer form, the high-dosage capsaicin patch, which a health care provider administers after applying a local anesthetic to the target area to minimize stinging and burning.

Six clinical studies (389 participants total) compared mild 0.075% capsaicin cream applied 3 to 4 times daily to painful sites with a placebo cream. Of participants who used the active cream, 41% experienced “some degree of pain relief,” compared with about 26% using placebo. The amount of pain relief varied among studies, from substantial (pain half gone or better) to undefined “improvement.” Two trials employed a single daily application of high-dose (8.0%) capsaicin cream via a patch that was left in place for 30 to 90 minutes. Of the 431 participants who received the high-dose capsaicin patch, 39% felt that it relieved their pain by at least one-third, compared with about 30% of the 278 participants administered placebo patches.

Conclusions & Commentary: The investigators concede that estimates of benefit and harm for capsaicin formulations are not robust due to limited amounts of data for different neuropathic conditions and inconsistent outcome definitions. Furthermore, true double blinding was a significant problem in the research trials, because capsaicin stings and burns while a placebo does not; trials attempted to overcome this by including other stinging ingredients in the placebos and there were noteworthy beneficial placebo effects reported. Although both active capsaicin formulations provided some pain relief, the numbers needed to treat (NNT) are not impressive: roughly 1 in 7 patients (NNT 95% CI; 4.1-17) may benefit from low dose capsaicin during 6 to 8 weeks, while only about 1 in 11 (6.4-70) benefit from the high-dose patch during 12 weeks. The wide confidence intervals reflect the different neuropathies examined and the relatively small numbers of subjects with each condition. At the same time, with the low-dose cream about 1 of every 2 patients experienced local skin reactions — burning, stinging, or redness — which can incur therapy discontinuation. There are few data examining the benefit-to-risk ratio of high-dose capsaicin, plus patients receiving the high-dose formulation require pretreatment with a local anesthetic. A further limitation of the trials was that there were no comparisons of capsaicin creams with counterirritants, such as Ben Gay® or Icy Hot®, available over-the-counter. The warm or cool sensations of these products distract from pain and they can be used on an as-needed basis, while capsaicin must be applied on a regular schedule.

Overall, the authors of this review suggests that, for patients suffering daily neuropathic pain, capsaicin therapy may provide some additional relief if they have failed to respond well or have proven intolerant of other treatments. For those patients, they wrote, “even a small degree of pain relief may be considered worthwhile.” Although, the reviewers still suggest that it might be best to consider capsaicin creams as an adjunctive or a secondary pain-relief measure, since there are oral medications for neuropathic pain with clear research evidence of effectiveness and tolerable side effects.

Reference: Derry S, Lloyd R, Moore RA, McQuay HJ. Topical capsaicin for chronic neuropathic pain in adults. Cochrane Database of Systematic Reviews. 2009(Oct);4(CD007393) [abstract here].