Over the last three decades, various approaches have been pursued to increase the retention of an oral dosage form in the stomach, including floating drug delivery systems (FDDS), swelling and expanding systems, bioadhesive systems, modified shape systems, high-density systems and other delayed gastric emptying devices (1). FDDS are widely explored for gastroretention purposes and have a bulk density lower than gastric fluids and thus remain buoyant in the stomach without affecting the gastric emptying rate for a prolonged period of time. While the system is floating on gastric contents, the drug is released slowly at a desired rate from the system (1, 2).Sodium alginate (SA) is a widely used natural polymer in various drug delivery systems. It exhibits favourable biological properties such as non-toxicity, biocompatibility, biodegradability and ulcer healing traits. Moreover, gelation of dilute solutions of SA occurs on addition of di-and trivalent metal ions by a co-operative process involving consecutive G-residues in the a-L-guluronic acid blocks of the alginate chain in a manner described by the 'egg-box' model (3). The procedure by which gelation is achieved is similar to the previously reported in situ gelling formulations of sodium alginate (4, 5).H 2 -antagonists or proton pump inhibitors are clinically used in treating chronic conditions like peptic ulcer and reflux oesophagitis. H 2 -antagonists competitively inhibit his- In the present work, a gastroretentive in situ gelling liquid formulation for controlled delivery of ranitidine was formulated using sodium alginate (low, medium and high viscosity grades), calcium carbonate (source of cations) and ranitidine. Prepared formulations were evaluated for viscosity, buoyancy lag time and buoyancy duration, drug content and in vitro drug release. Formulation variables such as concentration of sodium alginate, calcium carbonate and drug significantly affected the formulation viscosity, floating behavior and in vitro drug release. Analysis of the release pattern showed that the drug release from in situ gel followed a diffusion mechanism.
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