• A J Singer and J E Hollander.
• State University of New York, Department of Emergency Medicine, University Medical Center, Stony Brook 11794-7400, USA.
• Acad Emerg Med. 1995 Oct 1; 2 (10): 884-8.

ObjectiveTo compare the levels of infiltration pain and local anesthetic effects of plain and buffered 1% diphenhydramine.MethodsA prospective, randomized, double-blind, paired study was performed using 30 adult volunteers. Intradermal injections (0.5 mL) of plain and buffered 1% diphenhydramine were made in the subjects' forearms, one in the left and the other in the right. The pain of infiltration was recorded on a previously validated 10-cm visual analog scale (VAS). The volunteers also were asked which injection was less painful. Sequential measurements of the diameter of anesthesia to pinprick were made at 1, 2, 5, 10, 15, 20, 25, and 30 minutes. The VAS scores and anesthetic diameters were compared for plain and buffered diphenhydramine using a paired Wilcoxon rank sum test.ResultsThere was no statistically significant difference between buffered diphenhydramine and plain diphenhydramine for pain of injection (23.5 +/- 19.2 mm vs 28.2 +/- 18.7 mm, p = 0.24). Repeated-measures analysis of variance for anesthetic diameters demonstrated no significant difference between buffered diphenhydramine and plain diphenhydramine (p = 0.87). At no single measurement period were the anesthetic diameters different.ConclusionsIn a study with a sample size large enough to detect an 11-mm difference in VAS scores (power = 80%), no difference was found in pain of infiltration and anesthetic effects when plain 1% diphenhydramine was compared with buffered 1% diphenhydramine. Buffering of diphenhydramine does not appear to result in a clinically significant reduction in the pain of infiltration.

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