The relation between epinephrine concentration and the anesthetic effect of lidocaine iontophoresis.

We assessed the effect of epinephrine at various concentrations on the anesthetic effect during lidocaine iontophoresis. A solution of 2% lidocaine with epinephrine in concentration of 1:80,000, 1:160,000, 1:320,000, 2% lidocaine plain and normal saline control was delivered to the medial antecubital skin for 10 minutes by iontophoresis with 1.0 mA of direct current. The pinprick test and the von Frey test were conducted to evaluate anesthetic effect. Pricking pain using visual analogue scale was significantly lower throughout the entire experiment compared with the baseline values and lasted for 60 minutes in groups with 1:80,000 and 1:160,000 epinephrine. The pressure pain thresholds (PPT) and the touch thresholds (TT) were significantly elevated in groups with 1:80,000 and 1:160,000 epinephrine compared with the baseline values. No significant elevations in the PPT and TT values were observed in the other groups. The present study revealed that the anesthetic effect was significantly enhanced in an epinephrine dose-related manner and the anesthetic effect of 2% lidocaine with 1:160,000 epinephrine was equivalent to the same anesthetic with 1:80,000 epinephrine.