A new multiple-unit oral floating dosage system. I: Preparation and in vitro evaluation of floating and sustained-release characteristics.

A multiple-unit type of oral floating dosage system, (a new type of floating pills which generate carbon dioxide gas) has been prepared in order to prolong the gastric emptying time (GET) of the preparation. The floating ability and the sustained-release characteristics of the system have been elucidated in vitro. The system was composed of sustained-release pills as seeds and double layers on the sustained-release pills. The inner layer was an effervescent layer containing both sodium bicarbonate and tartaric acid. The outer layer was a swellable membrane layer containing mainly polyvinyl acetate and purified shellac. When the system was immersed in water, it formed swollen pills, like balloons, with a density much lower than 1.0 g/mL. The reaction was due to carbon dioxide gas generated by neutralization in the effervescent layer with the diffusion of water through the swellable membrane layer. The system was floating completely within approximately 10 min and approximately 80% remained floating over a period of 5 h irrespective of pH and viscosity of the test medium. While the system was floating, a drug (p-aminobenzoic acid) was released. The release rate of the drug from the system was zero order and depended on the sustained-release characteristics of the sustained-release seeds composing the system. The release rate was not affected by the amount of the swellable membrane layer up to 13% (w/w).