Background and objectives: The kinetics of insulin absorption exhibits considerable inter- and intra-individual variability, contributing to notable fluctuations in glycemic levels. Available methods for the evaluation of insulin absorption rely on measurements in the bloodstream. Currently, there is a lack of studies on in-vivo or non-invasive direct measurement of the absorption rate of the insulin administered subcutaneously. This study proposes a novel measurement method based on impedance spectroscopy to indirectly measure insulin absorption by measuring the insulin disappearance from the injection site and passage into the blood flow. Specifically, the goal of the study was to verify the sensitivity of the measurement method in transducing variation of drug amount in the investigated domain and variation of impedance magnitude. Methods: Four pre-gelled electrodes (dimensions: 2×7 mm) are positioned around the insulin injection site on the arm with an inter-electrode distance of 1 mm between the amperometric and voltmetric electrode and an inter-electrode distance of 4 mm between the voltmetric electrodes. As shown in the Figure, referring to a measurement in a healthy volunteer, the impedance of the arm was measured at serial intervals both before and after the injection of 100 µl of Lilly saline solution for insulin®. The excitation signal amplitude was set at 100 mV, with a frequency of 10 kHz. Results: As shown in the Figure, a 20 Ω notable decrease in the impedance magnitude of the arm tissue was registered after saline injection, followed by a decline to a minimal value (attributed to drug diffusion within the tissue under test) and a return to the pre-injection value after 120 minutes (indicative of drug absorption from the tissue). Conclusion: The observed impedance trend is consistent with the assumed saline absorption kinetics. Current investigations are extended to injecting insulin individuals with diabetes.
