A history of the use of Capsicum spp. and the predominant active ingredient, capsaicin, the parent compound of a group of vanillyl fatty acid amides, is presented. Distinct structural differences are noted between this compound and the capsaicinoids, especially the synthetic analog nonivamide, which has appeared as an adulterant in capsaicin-labeled products. Analysis shows that although some of these synthetic analogs eventually may prove to be true natural products, conclusive evidence based on isolation and structure elucidation is still absent after decades of attempted isolation from several potential natural sources. Although the crude, dark oleoresin extract of capsicum contains over 100 distinct volatile compounds and therefore may function in many ways dissimilar to capsaicin, the oleoresin continues to be marketed in products with a high degree of variability in efficacy. Capsaicin as a pure white crystalline material, however, acts specifically by depleting stores of substance P from sensory neurons, and has been successful in the treatment of several painful conditions (e.g., rheumatoid arthritis, osteoarthritis, peripheral neuropathies.
Twenty-five patients with symptomatic osteoarthritis (OA) of the knee were treated topically for one week with either 10% trolamine salicylate cream or placebo cream in a randomized double-blind crossover study. No significant difference was found in subjective or objective measures of pain relief between the treatment and control groups. Eight patients preferred "active" test cream, six preferred placebo, and 11 had no preference. No side effects were reported. Topically applied 10% trolamine salicylate cream did not relieve the pain of OA of the knee any more than did placebo.
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