An Overview: The Evaluation of Formation Mechanisms, Preparation Techniques and Chemical and Analytical Characterization Methods of the In Situ Forming Implants

One of the major developments of the last decade is the preparation of in situ implant formulations. Injectable, biocompatible and/or biodegradable polymer-based in situ implants are classified differently due to implant formation based on in vivo solid depot or formation mechanisms inducing liquid form, gel or solid depot. In this review, published studies to date regarding in situ forming implant systems were compiled and their formation mechanisms, materials and methods used, routes of administration, chemical and analytical characterizations, quality-control tests and in vitro dissolution tests were compared in Tables and were evaluated. There are several advantages and disadvantages of these dosage forms due to the formation mechanism, polymer and solvent type and the ratio used in formulations and all of these parameters have been discussed separately. In addition, new generation systems developed to overcome the difficulties encountered in in situ implants have been evaluated. There are some approved products of in situ implant preparations that can be used for different indications available on the market and the clinical phase studies nowadays. In vitro and in vivo data obtained by the analysis of the application of new technologies in many studies evaluated in this review showed that the number of approved drugs to be used for various indications would increase in the future.