Conditioning following powder micronization: influence on particle growth of salbutamol sulfate

Micronization is a high-energy process that induces changes in the crystallinity of materials. As a result, the crystalline structures on the particles' surface are being destroyed and amorphous areas are formed. After micronization of salbutamol sulfate to be used in dry powder inhalers, only small amounts of amorphous material are produced. Nevertheless, even these small amounts can have important effects on the physical stability of the powder. The amorphous state is thermodynamically unstable and tends to convert to the stable, crystalline state. The recrystallization process of disordered regions on the particles' surface leads to particle growth of milled particles. In this case, bridges of solid material are being formed between the individual particles, which leads to particle growth. This is an undesirable process, because particles for pulmonary administration are designed to range between 1 and 10 microm in diameter to exert respirative effect. In the present investigation, salbutamol sulfate is micronized by an air jet mill, and the generated products are exposed to different conditions. Thereafter, the best possible conditioning parameters and storage conditions for the micronized salbutamol sulfate are worked out and rated. The aim of this treatise is to demonstrate the importance of conditioning following micronization.