Evaluation of porous carrier-based floating orlistat microspheres for gastric delivery.

The purpose of this research was to prepare floating microspheres consisting of (1) calcium silicate as porous carrier; (2) orlistat, an oral anti-obesity agent; and (3) Eudragit S as polymer, by solvent evaporation method and to evaluate their gastro-retentive and controlled-release properties. The effect of various formulation and process variables on the particle morphology, micromeritic properties, in vitro floating behavior, percentage drug entrapment, and in vitro drug release was studied. The gamma scintigraphy of the optimized formulation was performed in albino rabbits to monitor the transit of floating microspheres in the gastrointestinal tract. The orlistat-loaded optimized formulation was orally administered to albino rabbits, and blood samples collected were used to determine pharmacokinetic parameters of orlistat from floating microspheres. The microspheres were found to be regular in shape and highly porous. Microsphere formulation CS4, containing 200 mg calcium silicate, showed the best floating ability (88% +/- 4% buoyancy) in simulated gastric fluid as compared with other formulations. Release pattern of orlistat in simulated gastric fluid from all floating microspheres followed Higuchi matrix model and Peppas-Korsmeyer model. Prolonged gastric residence time of over 6 hours was achieved in all rabbits for calcium silicate-based floating microspheres of orlistat. The enhanced elimination half-life observed after pharmacokinetic investigations in the present study is due to the floating nature of the designed formulations.