Formulation of Extended-Release Metformin Hydrochloride Matrix Tablets

Purpose: To develop and characterize an oral extended-release matrix tablet of metformin hydrochloride using a combination of a hydrophobic carrier and a hydrophilic polymer, and two types of formulation techniques. Methods: Various metformin hydrochloride formulations containing a hydrophobic carrier (stearic acid) and a hydrophilic polymer (polyethylene oxide) were prepared using a 32 factorial design. Two types of formulation techniques – melt granulation and direct compression – were evaluated. The influence of the carrier, polymer and preparation method on metformin release from the formulations in vitro as well as other physicochemical properties were studied. The release data were subjected to various release kinetic models and also compared with those of a commercial brand. Results: The physicochemical characteristics of all the granules and tablets were generally satisfactory. Optimization results indicate that the release rate of metformin HCl was directly proportional to the levels of stearic acid (SA) and polyethylene oxide (PEO) in the tablet formulations. Release rate was also dependent on the method of granulation used. Kinetic analysis showed that the formulation containing 30 %w/w of polymer exhibited release similar to that of the commercial brand with a similarity factor (f2) of 81.1. Melt granulation was more effective in extending drug release than direct compression. Release mechanism followed most closely the Korsemeyer-Peppas model with a correlation coefficient (r2) and 0.991. Conclusion: The use of a hydrophobic carrier along with a hydrophilic polymer effectively controls the initial rapid release of a highly water soluble drug such as metformin HCl. Hot melt granulation method was especially more effective in achieving this than the direct compression method.