Capsaicin is the spicy ingredient in chili pepper. It can deplete substance P from the terminals of afferent C-fibers, potentially leading to decreased pain perception. Capsaicin creams are effective in reducing post surgical pain in cancer patients. When applied topically, it may initially release substance P and cause severe burning pain. The pain related to the use of capsaicin gradually decreases over a few days, if the cream is applied regularly. A lower concentration cream (0.025%) or the application of a topical local anesthetic may help some patients decrease the initial burning pain, and tolerate the medication better. It is important to warn patients not to get any trace of the cream on mucous membranes since this causes severe pain.
Lidocaine patch 5% has been approved in the United States for the treatment of postherpetic neuralgia. Clinical experience supports the use of lidocaine patch 5% for other chronic pain conditions, especially when the pain affects a limited area. There is minimal systemic absorption. The patch is usually applied 12 hours per day with minimal systemic side effects. Topical lidocaine ointment in various concentrations (up to a compounded formulation of 10%) may offer a cost-effective alternative.