In the present study, an attempt was made to design and evaluate bilayer gastroretentive drug delivery system exhibiting a combination of an immediate release layer and a sustained release mucoadhesive layer as second layer to prolong residence time in stomach using Metformin HCl as a model drug to reduce frequency of administration and to overcome bioavailability problems. A total of 5 formulations of bilayer tablets containing the drug were prepared by direct compression method using 5 different mucoadhesive polymers in 5 different formulations (F 1 -F 5 ) respectively to impart mucoadhesion. Formulated bilayer tablets were evaluated by different parameters such as; ex vivo mucoadhesion strength, ex vivo mucoadhesion time, In vitro drug release study. In vitro drug release data were fitted to various kinetic models (Zero order, 1 st order, Higuchi model, Korsmeyer-Peppas model). Upon R 2 value analysis it was observed that release from F 1 , F 3 , F 5 followed Higuchi model and F 2 , F 5 followed Korsmeyer-Peppas kinetic model. Mechanism of drug release was found to be Fickian diffusion (value of n <0.45). F 4 with Na CMC was found to be more promising in ex vivo mucoadhesion study showing residence time of 4.08 hrs. This study concludes that formulated bilayer tablets were satisfactory in providing prompt release from 1 st layer then maintained sustained release effect with promising mucoadhesion behavior in stomach.Copy Right, IJAR, 2017,. All rights reserved. …………………………………………………………………………………………………….... Introduction:-The new drug delivery system with better efficacy and safety with reduced dosing frequency and improved patient compliance is the current area of research by formulation development scientists. Tablet being most preferred dosage form for its ease of manufacturing and patient convenience is always a first choice of dosage form. The single layer tablets leads to frequent dosing and unpredicted plasma level for drugs with shorter half-lives. Number of diseases require immediate release of drug for instant effect and then plasma concentration has to be maintained for prolong effect of the drug. So, in order to deliver drugs in a predictable time frame, multilayered oral controlled release delivery systems are designed. These systems enhance the efficacy, minimize the adverse effects and increase the bioavailability of drugs.

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