Contraceptive devices: subcutaneous delivery systems

Ever since natural sex hormones have been identified, their structure defined and their synthesis achieved, it became clear that their circulating half-life was too short to allow use in therapy. One of the modalities most thoroughly investigated to prolong their duration of action is to embed them in a polymeric matrix and administer them subcutaneously. Research and development activities of devices to be inserted under the skin have focused upon two modalities: the first utilizes the so-called nonbiodegradable devices, in which the matrix is fixed and the drug is made available through diffusion. In the second, biodegradable devices, the matrix dissolves during the process and both the active compound and the matrix components reach the circulation. Although a number of biodegradable systems have been investigated in the form of polymeric rod or micropellets, so far no system has reached the marketplace. Several matrices have been evaluated: poly(ortho esters), (polylactic-polyglycolic acid)co-polymers, poly-(ε-caprolactone). In the case of nonbiodegradable systems, several have been in widespread use for years. The first such system, Norplant® 1, consists of six capsules delivering levonorgestrel and lasts a minimum of 5 years; the second, called Norplant 2 (Jadelle®), consists of only two rods delivering the same amount of steroid of the first system, for the same duration of time. A third system already on the market is made up of a single rod releasing etonogestrel, the active metabolite of desogestrel, with duration of action of 3 years. Additional systems are still at the premarket stage. Subcutaneous implants have several obvious advantages, first and foremost their duration of action that can extend to at least 5 years, making them especially suitable for family-planning programs in developing countries; in addition, they are user- independent, again a positive feature in certain settings. Among the disadvantages, is a relatively complex insertion procedure that, for older systems, required ad hoc trained personnel and a small incision, clearly a disincentive. Newer devices, however, require a much simpler insertion procedure. Extracting systems is also complex and if a woman is lost to follow-up, implants will remain in the subcutaneous tissue forever.