Comparison of physical and inhalation properties of spray-dried and micronized terbutaline sulphate

Terbutaline sulphate particles, for use in dry powder inhaler formulations, were prepared by spray-drying, using a Büchi 190 mini spray dryer. Spray-drying conditions were chosen to allow the production of spray-dried terbutaline sulphate with a size similar to micronized terbutaline sulphate, that is to say about 2.9 μm of volume mean diameter. The physical properties and in vitro inhalation behaviour of micronized and spray-dried terbutaline sulphate were compared. X-ray diffraction, DSC, SEM and laser size analysis were investigated. Spray-dying produced spherically shaped particles with amorphous structure.After blending with different lactoses, adhesion and aerodynamic properties were investigated. Evaluation of adhesion was carried out with a mechanical sieve and an Alpine air-jet sieve. The adhesion of terbutaline sulphate on the lactoses tested was lower in the case of the spray-dried drug. Aerodynamic evaluation of fine particle dose and emitted dose was conducted using a twin stage impactor. The emitted doses and the fine particle doses were higher with the spray-dried terbutaline sulphate.The Alpine air-jet sieve assays showed that there was a correlation between drug separation from a carrier by sieving and that obtained from longer in vitro deposition studies. There was a linear relationship between the adhesion characteristics and the fine particle dose.