Controlled and sustained drug delivery has become the necessity in modern Pharmaceutical design and an intensive research have been undertaken in achieving much better drug product effectiveness, reliability and safety. This problem has been solved by insitu drug delivery system. In situ forming polymeric formulations are drug delivery systems that are in sol form before administration in the body, but once administered, undergo gelation in situ, to form a gel. They have been of recent interest due to the advantages exhibited by them: sustained and prolonged action in comparison to conventional drug delivery systems, ease of administration and reduced frequency of administration, improved patient compliance and comfort. The formation of gels depends on factors like temperature modulation, pH change, presence of ions and ultra violet irradiation, from which the drug gets released in a sustained and controlled manner. Mainly in situ gels are administered by oral, ocular, rectal, vaginal, injectable and intraperitoneal routes. Hydrogels are presently under investigation as delivery system for bioactive molecules, because of their similar physical properties as that of living tissue, which is due to their high water content, soft and rubbery consistency, and low interfacial tension with water or biological fluids. The article presents a detailed review of these types of polymeric systems, theirevaluation, advancements and their commercial formulations. Various biodegradable polymers that are used for the formulation of in situ gels include gellan gum, alginic acid, xyloglucan, pectin, chitosan, poly (DLlacticacid), poly (DL-lactide-co-glycolide) and poly-caprolactone. Different methods of preparation of hydrogels, novel methods of crosslinking used in the preparation of hydrogels, the mechanism of water transport through the ionic hydrogels, and the release mechanism of the solute from the hydrogels have been mentioned. The production of such devices is less complex and thus lowers the investment and manufacturing cost. These types of polymeric systems, their evaluation, advancements and their commercial formulations have been explained in detail in the article.
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