REVERSE IONTOPHORESIS - NONINVASIVE GLUCOSE MONITORING IN-VIVO IN HUMANS

Purpose: To demonstrate that ''reverse iontophoresis'' can be used to noninvasively obtain information about systemic glucose levels in vivo in humans. Methods. The passage of current across the skin in vivo dr ives ions into the tissue, from the electrode chambers positioned on t he skin surface, and simultaneously pulls ions from the body in the op posite direction. Because of the net negative charge on the skin, unde r normal conditions, the membrane is permselective to cations, and a p otential gradient also results, therefore, in electroosmotic convectio n of Solvent in the direction of counterion flow (i.e., from anode to cathode). Thus, it is also possible to enhance the transport of polar, yet uncharged, species using iontophoresis: In an earlier study, the in vitro extraction of glucose, by ''reverse iontophoresis'' was estab lished, and extension of the approach to an in vivo model was indicate d. The idea has therefore been further explored in vivo in humans. Res ults. Using small, simple, prototypical electrode chambers, attached t o the ventral forearm surface, direct current iontophoresis at 0.25 mA /cm(2) for periods of up to 1 hour, and a sensitive analytical procedu re to measure the quantities of glucose extracted, it has been shown t hat iontophoretic sampling of glucose is feasible. However, the shorte r periods (15 minutes or less) of extraction considered yield results which are ''contaminated'' (it is believed) by glucose that is a produ ct of lipid metabolism within the skin. While this material is expecte d to complicate the initial calibration of the approach, the problem i s effectively resolved within one hour, by which time the glucose arri ving in the electrode chambers on the skin surface is expected to dire ctly reflect the subcutaneous tissue concentration. Conclusions. Based upon these initial observations, further investigation can now be dir ected towards optimization of electroosmotic flow and sampling time, i mproved reproducibility and the development of a practical assay metho dology.