• Alan Silberberg, Tobias Moeller-Bertram, and Mark S Wallace.
• Department of Anesthesiology, University of California San Diego, San Diego, California, USA.
• Pain Med. 2015 Apr 1;16(4):745-52.

ObjectiveThe purpose of this study was to evaluate pain and hyperalgesia in response to different depths of intradermal (ID) capsaicin injections in healthy volunteers.DesignDouble-blind, cross-over study.SettingClinical Research Laboratory.SubjectsFifteen healthy male subjects received ID capsaicin injections into the volar aspect of each forearm at depths of 1 mm, 3 mm, 5 mm, and 7 mm. After injection, spontaneous pain, elicited pain, flare response, heat thresholds, and area of hyperalgesia were measured at various time points.Outcomes MeasureSpontaneous pain, elicited pain (pinprick, stroking, and hot pain), hyperalgesia area, and allodynia area.ResultsNo significant difference was found between any depths in spontaneous pain, elicited pain (pinprick, stroking, hot pain), hyperalgesia area, or allodynia area. A significant difference was found in the change in heat threshold between 5 mm and 1 mm, 7 mm and 1 mm, 5 mm and 3 mm, 7 mm and 3 mm depths. A significant difference was found in flare area between 5 mm and 3 mm depths. A significant difference was found in systolic blood pressure area under the curve (AUC) between 7 mm and 1 mm depths, and for both systolic and diastolic pressures for 5 mm and 1 mm depths, and 5 mm and 3 mm depths. A significant difference was found in pulse AUC between 5 mm and 1 mm depths and 5 mm and 3 mm depths.ConclusionsInjection of capsaicin at different depths in the skin had different effects on heart rate and blood pressure but no effect on pain. These results may have implications on the pharmacology and analgesic predictive value of the model of ID capsaicin.Wiley Periodicals, Inc.

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