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Can Topical Capsaicin Be A Treatment Alternative For Neuropathic Pain?

Neuropathic pain can result from several etiologies including nerve trauma, radiculopathy, postherpetic neuralgia and diabetic peripheral neuropathy. Despite these different etiologies, neuropathic pain shares common mechanisms including nerve damage and resultant hyperexcitability of peripheral nerves.

Treatment modalities for neuropathic pain have had variable success. Medications to treat neuropathic pain include neuroleptic drugs, antidepressants, opioids, ion-channel blockers and topical medications. Common side effects of oral medications for neuropathic pain include: weight gain, drowsiness, gastrointestinal disturbance, abuse and dependence. In many patients, the side effects of these medications lead to the discontinuation of their use.

Topical capsaicin is another treatment modality clinicians may consider for neuropathic pain.1-3 Capsaicin is produced from chili peppers and binds nociceptors in the skin, causing an initial stimulation of C fibers and the release of substance P. Researchers believe that repeat applications of capsaicin deplete substance P, resulting in nerve desensitization.3,4

Several studies have examined the use of capsaicin in the treatment of neuropathic pain. Mason and colleagues performed a review of randomized, controlled trials examining the use of capsaicin for the treatment of chronic neuropathic and musculoskeletal pain in adults.3 This study examined six double-blind placebo controlled trials utilizing 0.075% capsaicin for the treatment of neuropathic pain. The authors found a relative benefit of 1.4 for topical capsaicin in comparison to placebo but the number needed to treat was 8.1.

Derry and coworkers recently completed a Cochrane Database review examining the use of high concentration capsaicin for the treatment of neuropathic pain.1,2 This review included six studies with 2,073 participants and compared high concentration capsaicin (8% capsaicin patch) to 0.04% topical capsaicin. The 8% capsaicin patch has a concentration approximately 100 times greater than standard capsaicin cream. Authors found the high concentration capsaicin to produce moderate to substantial pain relief in patients with several types of neuropathic pain in comparison to controls. Patients who did experience pain relief with capsaicin often showed additional improvement in sleep, fatigue, depression and quality of life.

Local adverse effects are common with the use of capsaicin. The most common adverse event is burning at the application site. Systemic side effects are extremely rare and limited to respiratory irritation.4 Adverse effects reportedly decrease with continued use.4

In Conclusion

Topical capsaicin offers a potential treatment modality for patients with neuropathic pain who cannot tolerate or wish to avoid oral medications. New formulations, including the 8% capsaicin topical patch, have the potential to improve the efficacy of capsaicin in the treatment of neuropathic pain. Capsaicin is generally well tolerated with very rare systemic side effects. Limitations of capsaicin include lack of efficacy (especially at lower doses), cost and the need for repeat application.

References

1.      Derry S, Rice AS, Cole P, Tan T, Moore RA. Topical capsaicin (high concentration) for chronic neuropathic pain in adults. Cochrane Database Syst Rev. 2017;1:CD007393.

2.      Derry S, Sven-Rice A, Cole P, Tan T, Moore RA. Topical capsaicin (high concentration) for chronic neuropathic pain in adults. Cochrane Database Syst Rev. 2013; 2:CD007393.

3.      Mason L, Moore RA, Derry S, Edwards JE, McQuay HJ. Systematic review of topical capsaicin for the treatment of chronic pain. BMJ. 2004;328(7446):991.

4.      Rains C, Bryson HM. Topical capsaicin. A review of its pharmacological properties and therapeutic potential in post-herpetic neuralgia, diabetic neuropathy and osteoarthritis. Drugs Aging. 1995;7(4):317-328.

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