VALIDATION OF DIPHENHYDRAMINE AS A DERMAL LOCAL-ANESTHETIC

Study objective: Although diphenhydramine has been recommended as an a lternate local anesthetic for patients claiming allergy to lidocaine, no prior placebo-controlled evaluations of diphenhydramine for dermal anesthesia have been performed. We sought to determine the relative ef ficacy of diphenhydramine compared to saline placebo and lidocaine. De sign: Prospective, randomized, double-blind, placebo-controlled clinic al trial. Setting and participants: Twenty-four healthy adult voluntee rs. interventions: Subjects received intradermal 0.5-mL injections of diphenhydramine 1 %, diphenhydramine 2%, lidocaine 1 %, and normal sal ine placebo in a randomized, double-blind fashion. Extent of anesthesi a (in mm2) was assessed at one, two, five, ten, 20, and 30 minutes. Pa in of initial infiltration was assessed with a visual analog scale. Me asurements and main results: Diphenhydramine 1 % produced greater anes thesia than placebo (P< .001) and equivalent anesthesia to lidocaine 1 % (P= .889). (Our sample size had 90% power to detect a difference of 30% from the peak anesthesia observed.) Diphenhydramine 2% was less e ffective than diphenhydramine 1 %; however, this difference was not st atistically significant (P= .295). Infiltration of either concentratio n of diphenhydramine was significantly more painful than either lidoca ine or saline (P less-than-or-equal-to .001 for all comparisons). No c linically important complications were noted. Conclusion: In this stud y of 24 adult volunteers, diphenhydramine 1 % was as effective as lido caine 1 % for achieving dermal local anesthesia, although injection wa s more painful. Although no clinically important complications were no ted in our study, the safety of diphenhydramine remains to be establis hed, especially in areas with poor collateral perfusion (eg, digits, p inna, and nose).