Microdialysis and Delivery of Iontophoresis-Driven Lidocaine Into the Human Gastrocnemius Muscle

Abstract

Iontophoresis is used frequently in physical medicine and rehabilitation, but many research techniques do not adequately measure it for depth of medicine delivery. To determine if iontophoresis delivers lidocaine 5 mm under the surface of human skin. Descriptive laboratory study. Therapeutic modalities research laboratory. Eight men and 5 women volunteers (age range = 21± 2.3 years) who had less than 5 mm of adipose tissue in the area we measured participated in the study. We inserted a microdialysis probe 5 mm under the skin of both legs and into the triceps surae muscle groups of 10 participants. Microdialysis was performed for 60 minutes to allow a recovery period for local skin blood flow to return to baseline. We then delivered 2 mL of 1% lidocaine to the treatment leg via iontophoresis at 40 mA/min. Next, microdialysis was performed continuously in both legs during the treatment and for 30 minutes posttreatment to collect the lidocaine samples. After we had gathered the samples, several saline solutions with various amounts of lidocaine (0.005%, 0.025%, 0.05%, and 0.1 %) were prepared in vitro and analyzed. Although we did not intend to do so as a part of the original study, we also performed an identical follow-up study at 3 mm in 3 participants. Both in vitro and in vivo samples were analyzed via reverse-phase high-performance liquid chromatography (RP-HPLC). A protocol for detection and quantification of lidocaine using RP-HPLC was followed. We did not detect any measurable levels or concentrations of lidocaine in the 10 control samples. According to the RP-HPLC analysis, the 10 treatment samples also were negative for the presence of lidocaine. However, when we performed the study at 3 mm, microdialysis detected lidocaine in the 3 participants at this depth in the treatment leg only. Measurable levels of lidocaine were not detected at 5 mm but were found at 3 mm. More studies are needed to determine the efficacy of microdialysis in measuring iontophoresis-delivered compounds.