STERILIZATION OF IMPLANTS <ul><li>Implants are usually introduced subcutaneously using a surgical procedure. </li></ul><ul><li>The need for surgery is an obvious disadvantage but, conversely, the device can also be removed when required or when exhausted of drug, which is an advantage. </li></ul><ul><li>Numerous shapes have been explored, from plates, long rods, and short rods to spheres, and newer bioerodable matrixes are coming into use. </li></ul><ul><li>For example: </li></ul><ul><li>poly(lactide-co-glycolide) (PLGA) was originally developed as an absorbable suture so that it has obvious advantages as an implant containing a drug. </li></ul><ul><li>The Norplant device has been introduced in which silicon rubber rods containing levonorsgestrel have been implanted under the skin with the aid of a local anesthetic. </li></ul>
Polymeric Implants Polymeric implants are commonly prepared from hydrogels,silicone rubbers, or other biocompatible materials. Hydrogels generally have an advantage in that they are able to swell in an aqueous medium without necessarily dissolving. This capacity for water is useful in that it promotes or improves compatibility with body tissues but it has been suggested that incorporated low molecular weight drug substances are able to diffuse out of the device without necessarily being rate-controlled. 3. For additional information see the chapter FERTILITY CONTROL. 4. Sub dermal injection of small rods or cylinders or even spheres through a cannula has some advantages, and these devices have also been evaluated clinically.
<ul><li>Sterilization of Polymeric Implants </li></ul><ul><li>Polymeric implants are readily made by extrusion of powdered components but application of heat would melt the polymer and affect the release properties of the device, assuming that the drug itself was stable enough for the purpose, -irradiation is effective and commonly used for this purpose because of the great deal of experience in the sterilization, for example, of PLGA suture threads. </li></ul><ul><li>Oxidizing gases such as peroxides are not suitable for sterilization of surfaces because, with a bioerodable implant, there is a need to sterilize throughout the structure of the implant, not just its surface. </li></ul><ul><li>Moreover, there is a real danger that these reactive chemicals produce chemical changes at the interface of both the biopolymer and its incorporated drug. </li></ul>