Formulation and Evaluation of Sustained Release Bilayer Tablets of Glimepiride and Metformin HCl.

Metformin is an oral antidiabetic biguanide drug for the treatment of type 2 diabetes, in particular, in overweight and obese people and those with normal kidney function. It is a class III high soluble, low permeable compound slowly and incompletely absorbed from the gastrointestinal tract and the absolute bioavailability of a single 500mg dose is reported to be 50%-60%. The compound also has relatively short plasma elimination half-life of 1.5 to 4.5 hrs, hence Metformin HCl has to be administered two or three times per day. Glimepiride is one of the third generation sulfonylurea drugs useful for control of diabetes. It maintains a more physiologic regulation of insulin secretion and the risk of hypoglycaemia is less than with other sulfonylurea. It‟s a white hydrophobic powder, practically insoluble in water; bioavailability is 100%, half-life is 5 hrs and available dose is generally 1mg or 2mg once a day. Glimepiride and Metformin simultaneously targets insulin resistance and insulin deficiency type II diabetes. The aim is to develop a combination drug therapy for anti diabetic tablet formulation having different mechanism of action to complement each other and together effectively lower blood glucose level. The immediate release layer of Glimepiride is prepared by direct compression method using SSG as superdisintegrant with other excipients and sustained release layer of Metformin HCl are prepared by wet granulation method using HPMC and Xanthan Gum as polymer in different concentration with other excipients. The present work was aimed towards developing a bilayer tablets containing Glimepiride as immediate release and Metformin HCl as sustained release. The tablets were prepared using techniques of wet granulation and compression. The optimization of the tablets was done based on experimental result such as its physiochemical parameters, dissolution and content uniformity. The tablets produced were stable and reliable. The result suggested that various variables affecting the dissolution of the tablets. Formulation F6 shows better dissolution. So it is suggested that for highly water soluble drug like Metformin HCl, it is desirable to use combination of different polymer for sustained release layer and incorporation of superdisintegrant like SSG in immediate release layer. The release data further indicated that combination of SCMC and HPMC K 100M can give the sustained release effect followed by the initially burst release effect due to the superdisintegrant SSG in immediate release layer. HPMC K100M polymer controlled the release of Metformin HCl up to 10 hrs intended for once daily administration. The release data of in vitro study indicates that formulation follows zero order, Higuchi equation and diffusion takes place via non-fickian transport. Formulation F6 found to be stable at accelerated stability as per the ICH guidelines for a period of 3 months. Finally it concluded that Glimepiride as immediate release and Metformin HCl as sustained release indicate promising potential of both drugs in the form of bilayer tablets an alternative to the conventional dosage form