Abstract: By combining analyte concentration monitoring electrodes and infusion functions into a single subcutaneous element, the described sensing cannulae having a rectangular cross-section avoids the need for two separate devices for insulin delivery and glucose concentration determination. The substantially flat, thus planar, surface of the sensing cannula provides a substrate for deposition of one or more sensing electrodes, preferably through a lithographic-type process. The inner lumen of the sensing cannula serves as a conduit for drug delivery and is formed in a manner that is compatible with lithographic-type electrode formation. The rectangular cross-section of the sensing cannula also allows face and side ports establishing fluid communication between the inner lumen and tissue that preferably reduces the incidence of occlusion of the inner lumen of the sensing cannula.