The effects of carrier size and morphology on the dispersion of salbutamolsulphate after aerosolization at different flow rates

We have investigated the interdependence of various factors (particle size, surface smoothness, carrier particle shape, inhalation flow rate) on the d eposition of a model drug (salbutamol sulphate) after aerosolization from a model inhaler device (Rotahaler). Different batches of a-lactose monohydrate were prepared to have different particle size, particle shape and surface smoothness. Each batch of lactose was then mixed separately with salbutamol sulphate in a ratio of 67.5:1 (w /w), under similar conditions. Drug deposition from each formulation was in vestigated using a 4-stage liquid impinger after aerosolization at 28.3, 60 .0 and 96.0 L min(-1) via a Rotahaler. At a flow rate of 28.3 L min(-1), a large portion of drug particles was not emitted from the inhaler, the % emission varying from 29.6% to 66.6% for a ll formulations investigated. Drug emission tended to increase with particl e size of the carrier whilst fine particle fraction, fine particle dose and dispersibility appeared to increase with decreasing particle size but incr easing elongation ratio of the carrier particles. Increasing the flow rate to 60.0 L min(-1) was shown to increase drug emission since >75% total dose was found to be emitted from the inhaler. Again, smaller or more elongated lactose particles resulted in a higher fine particle dose or fine particle fraction of salbutamol sulphate than the coarser carrier, although they pr oduced a similar (analysis of variance P>0.05) drug emission. Increasing th e flow rate to 96.0 L min(-1) did not increase drug emission. Increasing th e flow rate resulted in an increase in the fine particle fraction and fine particle dose of salbutamol sulphate from all formulations. The flow rate o f the airstream appeared to play the most important role, followed by parti cle size and elongation ratio of the carrier particles, with the surface sm oothness relatively less significant in determining the deposition of salbu tamol sulphate from the Rotahaler.