Iontophoresis as an adjunct to EMLA cream for local anesthesia

Purpose. Local anesthesia is commonly used for eyelid surgery, yet the injection of the acidic lidocaine solution often causes discomfort. EMLA cream (lidocaine and prilocaine) applied topically provides local anesthesia, but takes one hour to achieve its effects. Iontophoresis enhances the effect of lidocaine solution. We studied the effect of iontophoresis as an adjunct to EMLA cream to lessen the discomfort of anesthetic injection and to speed the onset of action. Methods. EMLA cream was placed on both forearms of 12 healthy volunteers. An iontophoretic current of 4.0 mAmp/min was applied to one forearm for 15 minutes in a masked fashion. Lidocaine 1% with epinephrine was injected at the site of EMLA cream. Subjects rated on a scale from 0 to 10 their degree of discomfort at 3 times: baseline; while receiving current; upon injection. Student's t-test was used for statistical analysis. Results. Baseline discomfort scores in all subjects were zero. 7 of 12 subjects reported less pain upon injection at the iontophoresis site while 5 of 12 reported no difference (mean 2.67 vs. control arm 3.69), however the difference was not statistically significant (p<.75). Subjects experienced some minor discomfort while receiving the current (mean 1.9 vs control arm 0.51), yet this also was not significant (p<.73). Conclusions. EMLA cream is an alkaline preparation with approximately 10% of the lidocaine in an ionized state. Iontophoresis should continuously drive the ionized drug into the skin allowing the unionized drug on the surface to reach a new equilibrium state, and hence make more ionized drug available. Although not statistically significant, our positive results indicate that further study is warranted in both altering the pH of EMLA cream and increasing the time of applied current.