Injectable In-situ Forming Drug Delivery Systems Based on Biodegradable Polymers

The ability to inject a drug-incorporated polymer to a localized site in which the drug transforms from a solution to a semi-solid drug depot has a number of advantages. Most notable among these advantages are ease of application and localized, prolonged drug delivery. In the area of parenteral controlled release formulations, in-situ forming formulations are attractive alternatives to preformed implants and microparticles. Biodegradable in-situ forming implants can be manufactured in simple steps with minimum equipments and uncomplicated processes. They are injected as low viscous solutions or suspensions and transform in the body to a gel or solid depot. Different ways can be used to stimulate this transformation: crosslinking, solidification or precipitation of polymer solution which the former produces in situ crosslinking systems, and the next one produces in situ solidifying organogels and the last one produces in situ polymer precipitation systems with phase separation .In this article we introduce the various strategies that are used to prepare in situ setting systems, and outline their advantages and disadvantages as localized drug delivery systems.