Gastroretentive Orlistat Microspheres: Formulation, Characterization, and In Vitro Evaluation

The present study involves the preparation and evaluation of floating microspheres of orlistat for improving drug bio-availability by prolongation of gastric residence time. The microspheres were prepared by a solvent diffusion-evaporation technique using inert polymers (Eudragit RL100, cellulose acetate, and ethyl cellulose). The effect of three formulation variables (i.e., drug/polymer ratio [DIP], polymer amount, and stirring speed) on floatability, encapsulation efficiency, percentage fines, and release mechanism were studied. The results of Fourier transform infrared spectroscopy show no interaction between the drug and the polymers. In vitro dissolution studies were performed in 0.1 N HCl (pH 1.2) for 12 h, and samples were analyzed by HPLC using a UV-vis detector at 205 nm. The grading curve was constructed for the selected formulations, and D(30), D(60), and D(90) values were determined to characterize the size distribution. A comparison of r(2) values for Higuchi, Korsmeyer-Peppas, and zero-order kinetic models for different batches of microspheres shows Fickian and non-Fickian diffusion kinetics. The orlistat microspheres prepared with cellulose acetate (DIP 1:2) at the stirring speed of 900 rpm show maximum floatability and optimum encapsulation efficiency, and exhibited a prolonged release for almost 12 h with a Fickian diffusion release mechanism.