THE COATING AND THE ENCAPSULATION OF AN INTERACTIVE POWDER MIXTURE AND ITS APPLICATION TO SUSTAINED-RELEASE PREPARATIONS

Abstract— Fine cohesive isoprenaline HCl particles adhered to the surface of coarser potato starch particles to form interactive mixtures. These were coated with magnesium stearate by dry mixing. To check if there was a lowering of homogeneity in the latter stage, the degree of mixing was investigated before and after adding magnesium stearate. The surface appearance of magnesium stearate‐coated interactive mixtures became smoother as mixing time increased or the temperature of the powder bed during mixing was raised. Ultimately, the magnesium stearate encapsulated the particles of interactive mixture. The coated interactive mixtures improved sustained release of isoprenaline HCl over the starch mixtures alone, the effect depending on the density of the magnesium stearate. Only in encapsulated mixtures was the release rate of drug decreased as the amount of magnesium stearate increased. The release of isoprenaline HCl from the interactive mixtures followed first‐order kinetics. A linear relationship existed between the first‐order rate constant and the reciprocal thickness of the magnesium stearate film, indicating a diffusion‐controlled system with the film having some pores. 1990 Royal Pharmaceutical Society of Great Britain