Randomized trial of diphenhydramine versus benzyl alcohol with epinephrine as an alternative to lidocaine local anesthesia

Study objectives: We compared the pain of infiltration and anesthetic effects of .9% benzyl alcohol with epinephrine, 1% diphenhydramine, and .9% buffered lidocaine. Methods: A prospective, randomized, double-blind study comparing benzyl alcohol, diphenhydramine, and lidocaine was carried out on adult volunteers. Each subject received all 3 injections in a standardized manner. Pain of infiltration was measured on a 100-mm Visual analog pain scale and analyzed with a Kruskal-Wallis test. Duration of anesthesia was assessed at 5-minute intervals for a maximum of 45 minutes and compared with the use of survival analysis techniques by a log-rank test. Return of sensation by 45 minutes was evaluated with an exact chi(2) test. All tests were 2-tailed, with significance defined as P<.05. Results: Thirty subjects were enrolled. The diphenhydramine median pain score was 55 mm, compared with 12.5 mm for lidocaine and 5 mm for benzyl alcohol (P=.001). Pairwise comparisons showed that all possible combinations were statistically significant. The 3 anesthetics were different with respect to duration of anesthesia (P<.001). Pairwise comparisons revealed a longer duration of anesthesia for lidocaine than for diphenhydramine or benzyl alcohol, but no significant difference was found between diphenhydramine and benzyl alcohol. Pain sensation returned within the 45-minute study period in only 3 of 30 lidocaine injections, compared with 11 of 30 benzyl alcohol injections and 19 of 30 diphenhydramine injections (P=.001). Conclusion: Benzyl alcohol is a better alternative than diphenhydramine as a local anesthetic for lidocaine-allergic patients.