Abstract

AN OVERVIEW ON – IN-SITU GEL FORMING IMPLANTABLE DRUG DELIVERY SYSTEMS

M. Mohan Varma, Ashok Thulluru, K. T. Sunil Kumar, K. Vijaya Durga, B. Anjana, G. Yamini Srinivas*

ABSTRACT

In the field of parenteral controlled release formulations, in-situ forming implants (ISFI) are engaging alternatives to preformed implants and microparticles. Liquid formulations generating (semi) solid depot after subcutaneous injection, are also designated as implants. These formulations show a number of applications for a number of reasons. The main application is less invasive and less painful compared to implants which required local anesthesia and a small surgical intervention. They are injected into body as a low viscous solution and transform into gel or solid depot. Many approaches can be used to stimulate this transformation: (1) In-situ cross-linking, (2) In-situ solidifying organ gels (3) In-situ polymer precipitation (4) Thermoplastic paste (5) Thermally induced gelling systems. The present review discusses the principles of each strategy. Even though the principle of ISFI is so much accomplished, important issues remain to be solved. They involve (i) toxicity issues (ii) variability of the implant shape and structure, and (iii) avoidance of burst release during the implant formation. Unluckily, until now the knowledge concerning the detailed process of the implant formation is still very short. This is because of the fact that the process of implant formation and degradation, drug release, interconnected, heterogeneous, tissue response are complex and not easy to follow, especially in vivo. New approaches and materials are entering the pre-clinical and clinical phases and it can be sure, that ISFI will pick up more importance within the future years.

Keywords: In-situ forming implants; In-situ cross linking; In-situ solidifying implants; In-situ polymer precipitation; Thermally induced gelling systems.