Comparison of iontophoresis of lidocaine with a eutectic mixture of lidocaine and prilocaine (EMLA) for topically administered local anesthesia.

BACKGROUND

Almost all dermatologic surgery is accomplished using local anesthesia. To make our patients more comfortable, there is a constant search for less painful methods of administering anesthetic agents. Topical EMLA as well as iontophoresis are both useful in this regard.

OBJECTIVE

In this study we compared topical EMLA with lidocaine delivered by iontophoresis in a double-blind placebo-controlled trial. Our goal was to assess the degree of anesthesia obtained as well as the relative rapidity of onset.

METHODS

A double-blind controlled study was performed on 10 healthy volunteers between 26 and 37 years of age. Three test sites were placed on each forearm. EMLA or a moisturizer control was placed on two of the three test sites on each arm. Each site was wiped free of cream and tested for sensitivity to pinprick 30 and 60 minutes after cream placement. One iontophoretic unit was placed on each forearm. Both units were saturated with anesthesia with the control unit being turned off. Sensitivity to pinprick was evaluated at the iontophoretic sites and one of the EMLA sites 30 minutes after site placement on the subject. The additional EMLA-treated site was tested in the same manner 60 minutes after placement.

RESULTS

Both EMLA cream and the iontophoretic unit delivered topical anesthesia greater than the control. Significantly more anesthesia was acquired 1 hour after application of EMLA than was seen 30 minutes earlier. The iontophoretic patch-treated area provided greater anesthesia than the EMLA-treated sites evaluated 30 and 60 minutes after placement. Both modalities provided significant anesthesia when left in place for 60 minutes.

CONCLUSION

Both iontophoresis of lidocaine and topical EMLA delivered significant, and sometimes complete, local anesthesia. A greater degree of anesthesia is delivered via iontophoresis after 30 minutes as compared with EMLA left on the skin for 30 or 60 minutes. Both modalities have important and unique advantages and disadvantages. Topical EMLA and iontophoretically delivered lidocaine are both valuable tools for the dermatologic surgeon.