Buoyancy and drug release patterns of floating minitablets containing piretanide and atenolol as model drugs

The purpose of this study was to evaluate factors for improving the in vitro buoyancy and the drug release characteristics of floating minitablets containing either piretanide or atenolol as model drugs. The buoyancy of the minitablets was achieved either by the swelling of the excipient or by incorporation of the gas-generating agent sodium bicarbonate. Resultant-weight kinetics were performed in order to evaluate the buoyancy. The release rate of the poorly soluble drug piretanide was enhanced by increasing its solubility or by promoting the erosion of the minitablets. For the sparingly soluble drug atenolol, the minitablets were coated with different ratio of insoluble polymer in order to diminish the release rate of this drug. The swelling of a hydrophilic excipient was not sufficient to obtain floating minitablets. The buoyancy of the minitablets containing either piretanide or atenolol was greatly improved by adding sodium bicarbonate as well as by a wet granulation. The most satisfactory improvement in the release rate of piretanide was achieved using a solid dispersion with povidone, thus increasing the drug solubility concomitantly with the increase of the minitablets' erosion. Regarding atenolol, minitablets containing 7% sodium bicarbonate and coated with Eudragit NE30D:RS 70:30 gave satisfactory results concerning buoyancy and drug release rate. This study showed that it was possible to produce minitablets containing either piretanide or atenolol, which have a positive resultant-weight during more than 6 hr and satisfactory release profiles.