Two‐Minute Skin Anesthesia Through Ultrasound Pretreatment and Iontophoretic Delivery of a Topical Anesthetic: A Feasibility Study

Background and Objectives.  The pain associated with percutaneous procedures is a significant source of distress in clinical practice, especially in children. Topical anesthetics require 30–60 minutes to provide skin anesthesia; with iontophoresis, they minimally require 10 minutes, and with ultrasound pretreatment, 5 minutes. In this study, we assessed the feasibility of providing skin anesthesia to needle prick with the combination of ultrasound pretreatment and 2‐minute low‐voltage (1 mA) iontophoresis. We compared it with sham‐ultrasound pretreatment and with standard, 10‐minute high‐voltage (4 mA) iontophoresis. Methods.  This is a single‐blind, randomized, controlled, crossover study in healthy volunteers, specifically for the purpose of the study subjected to standardized needle prick. They rated the absolute pain associated with the needle prick on a 10‐cm visual analog scale, with 0 being “no pain” and 10 being “extremely painful.” Results.  Of the 31 subjects who consented to the study, 30 were randomized and completed the study. The mean duration of the ultrasound pretreatment was 21.4 seconds (range: 6–85). The absolute pain scores for the ultrasound plus 2‐minute low‐voltage iontophoresis and the standard, 10‐minute high‐voltage iontophoresis were not statistically significantly different (0.9 ± 0.31 vs 0.46 ± 0.20; P  = 0.49). However, they were statistically significantly different from the sham‐ultrasound plus 2‐minute low‐voltage iontophoresis pain score (2.6 ± 0.55) ( P  = 0.0001 and 0.0012, respectively). Conclusions.  Ultrasound pretreatment plus 2‐minute low‐voltage iontophoresis provides better skin anesthesia than sham‐ultrasound plus 2‐minute low‐voltage iontophoresis, and similar to standard, 10‐minute high‐voltage iontophoresis.