Effect of EMLA pre-treatment on capsaicin-induced burning and hyperalgesia.
Capsaicin, which has been studied extensively as a treatment for itch and several chronic pain disorders, induces burning during the first week of therapy, 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 capsaicin effects on thermal sensation and pain thresholds. Healthy adult volunteers participated in the single-blind, 6-day study. After baseline measurement of warmth, cold pain and heat pain thresholds with a computerized thermal sensory analyzer, subjects applied EMLA thrice daily on one forearm and vehicle placebo on the other forearm, 60 min before applying capsaicin 0.075% on both forearms. Subjects rated burning sensations 3 times a day throughout the study. After 1 and 5 days of thrice daily application of EMLA or vehicle followed by capsaicin, thermal sensory testing was repeated. Subjects rated burning sensations to the significantly less on the EMLA pre-treated forearm compared with the placebo pre-treated forearm during all 5 days of treatment (p < 0.01). Capsaicin with and without EMLA produced significant heat pain hyperalgesia and cold pain hypoalgesia after 1 day of treatment. After 5 days of treatment, heat pain hyperalgesia persisted on both forearms; however, it was significantly less on the EMLA-treated forearm vs the vehicle-treated site (p < 0.03). Cold pain hypoalgesia persisted in both forearms. The warmth sensation threshold was significantly higher on the EMLA-pre-treated forearm after 1 and 5 days of treatment. In conclusion, pre-treatment with EMLA significantly reduced the burning sensation from capsaicin and attenuated heat hyperalgesia during treatment.
Yosipovitch
G
G
Department of Dermatology, Rabin Medical Center, Israel.
Maibach
H I
HI
Rowbotham
M C
MC
D000279:Administration, Cutaneous; D000328:Adult; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology*; D002211:Capsaicin / Q000009:adverse effects*; D005260:Female; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced / Q000517:prevention & control*; D008012:Lidocaine / Q000008:administration & dosage / Q000494:pharmacology*; D000077442:Lidocaine, Prilocaine Drug Combination; D008297:Male; D008875:Middle Aged; D017288:Pain Threshold / Q000187:drug effects*; D010292:Paresthesia / Q000139:chemically induced / Q000517:prevention & control*; D011292:Premedication; D011318:Prilocaine / Q000008:administration & dosage / Q000494:pharmacology*; D012016:Reference Values; D012720:Severity of Illness Index; D016037:Single-Blind Method; D016896:Treatment Outcome
D000779:Anesthetics, Local; D000077442:Lidocaine, Prilocaine Drug Combination; D011318:Prilocaine; D008012:Lidocaine; D002211:Capsaicin