Double-blinded comparison of diphenhydramine versus lidocaine as a local anesthetic.

STUDY

OBJECTIVE

To evaluate the efficacy, onset of action, duration of action, and side effects of 1% diphenhydramine compared with 1% lidocaine when used as a local anesthetic agent.

DESIGN

Prospective, double-blinded, cross-over study.

SETTING

Emergency medicine residency program, research section.

PARTICIPANTS

Ten healthy male volunteers, aged 26 to 38 years old.

INTERVENTIONS: Baseline levels of sensation to pinprick (18-gauge needle) within a 2.4-cm-diameter midvolar forearm area and levels of sedation were recorded on 10.2-cm visual analog scales. Subjects then underwent subcutaneous infiltration of 20 mg (2 mL) of the study agent using a 27-gauge needle. Visual analog scale sensation and sedation scores were recorded at five, ten, and 15 minutes and then every 15 minutes until return to baseline. Subjects were studied one week later with the alternate agent. Nonparametric data were analyzed using the Mann-Whitney U test with significance at P < .05.

RESULTS

No significant differences in mean pinprick sensation were seen from baseline to 30 minutes. Significant differences were seen at 45 (P = .036) and 60 minutes (P = .036). The mean duration of effective anesthesia was significantly longer for lidocaine than diphenhydramine (81 versus 42 minutes, P = .028). No significant differences were seen in the sedation scores or in the frequencies of local reactions. One subject developed skin necrosis at the injection site with diphenhydramine.

CONCLUSION

The duration of local anesthesia for 1% lidocaine was significantly longer and the depth of anesthesia after 30 minutes was significantly higher than that of 1% diphenhydramine. Diphenhydramine resulted in skin necrosis in one test subject.