Sandwiched osmotic tablet for controlled release of metoprolol succinate

In this study novel concept of osmotically controlled drug delivery system in the form of three layered sandwiched tablet (SOT) was introduced. The tablets were prepared and optimized by design of experiment method. Metoprolol succinate, an antihypertensive agent, was selected model drug. Modified Ishikawa diagram was used to understand critical parameters that might affect the final product. Sandwiched osmotic tablets were prepared by direct compression and coated with cellulose acetate film. The process and formulation parameters were initially screened by Plackett–Burman design and later optimized by Box Behnken design. From the tablets we evaluated hardness, friability, weight variation, weight gain, coating uniformity and in vitro drug release as critical quality attributes. The amount of sodium chloride, polyethylene oxide and hydroxypropyl methylcellulose were found to influence the drug release rate from SOT as evident from Plackett–Burman design. Further these factors were optimized to get extended drug release of 80 % or more in 20 h. Optimized formulation batches (BBD8 and BBD5) showed drug release of 79.62 ± 1.19 and 82.46 ± 0.45 % respectively in 20 h with diffusion controlled zero order drug release. The check point batch prepared showed drug release of 80.86 % in 20 h. The prepared osmotically controlled sandwiched tablet showed potential to control the drug release with zero order kinetics.