Effect of EMLA pre-treatment on capsaicin-induced burning and hyperalgesia

Capsaicin, which has been studied extensively as a treatment for itch and s everal chronic pain disorders, induces burning during the first week of the rapy, causing a substantial percentage of patients to discontinue treatment prematurely. We examined whether pre-treatment with the topical anesthetic EMLA reduces the burning sensation induced by capsaicin and alters capsaic in effects on thermal sensation and pain thresholds. Healthy adult voluntee rs participated in the single-blind, 6-day study. After baseline measuremen t of warmth, cold pain and heat pain thresholds with a computerized thermal sensory analyzer, subjects applied EMLA thrice daily on one forearm and ve hicle placebo on the other forearm, 60 min before applying capsaicin 0.075% on both forearms, Subjects rated burning sensations 3 times a day througho ut the study, After 1 and 5 days of thrice daily application of EMLA or veh icle followed by capsaicin, thermal sensory testing was repeated, Subjects rated burning sensations to be significantly less on the EMLA pre-treated f orearm compared with the placebo pre-treated forearm during all 5 days of t reatment (p < 0.01). Capsaicin with and without EMLA produced significant h eat pain hyperalgesia and cold pain hypoalgesia after 1 day of treatment. A fter 5 days of treatment, heat pain hyperalgesia persisted on both forearms ; however, it was significantly less on the EMLA-treated forearm vs the veh icle-treated site (p < 0.03). Cold pain hypoalgesia persisted in both forea rms. The warmth sensation threshold was significantly higher on the EMLA-pr e-treated forearm after 1 and 5 days of treatment. In conclusion, pre-treat ment with EMLA significantly reduced the burning sensation from capsaicin a nd attenuated heat hyperalgesia during treatment.