DESIGN AND EVALUATION OF GASTRORETENTIVE SUSTAINED RELEASE BILAYER TABLET OF METFORMIN HCl USING RICE BRAN WAX MATRIX

Background: The present study deals with the formulation of floating bilayer tablet of Metformin HCl, a biguanide class of antidiabetic.

Materials and Methods: The gas releasing component, necessary for the tablet to float, is put in the food grade rice bran wax matrix and the delayed release component HPMC was put in a separate layer of the bi-layer matrix tablet. The tablet blends were evaluated for their properties like Carr’s Index and Hausner’s ratio and compressed into a bilayer tablet. The tablets were evaluated for their properties like physical properties, drug content, buoyancy lag time, buoyancy time, dissolution rate and kinetics of drug dissolution.

Results and Discussion: The blends showed good flow properties (Carr’s Index in range 11-26, Hausner’s ratio 1.12-1.35). The tablets had good crushing strength (Friability below 1%) and good physical properties. The gas released made the tablet buoyant with the buoyancy lag times (BLT) decreased with increase in the rice bran wax amount of the layer (BLT in range of 30 sec decreased to about 7 sec). This layer erodes slowly as the tablet floats with effervescence and the wax layer being less dense keeps the tablet buoyant for almost 6 hrs. The drug release from the HPMC matrix is delayed for nearly 10 hrs. The drug release kinetic studies suggested a first order mechanism with case two transport being the mechanism of drug release.

Conclusion: It can be concluded from the literature that the concentration in which HPMC is utilized in the delayed release layer can be mucoadhesive. Thus the bilayer tablet shall remain intact in the upper GIT, where the drug has preferential absorption site. This shall improve the bioavailability of the drug.