EFFECT OF DRUG LOAD AND PLATE COATING ON THE PARTICLE-SIZE DISTRIBUTION OF A COMMERCIAL ALBUTEROL METERED-DOSE INHALER (MDI) DETERMINED USING THE ANDERSEN AND MARPLE-MILLER CASCADE IMPACTORS

Purpose. The purpose of this study is to investigate the effect of dru g load, the coating of impactor stages, and the design of cascade impa ctors on albuterol MDIs particle size distribution measurements. The r esults of the investigation will be used to explain the ''loading effe ct'' recently reported. Methods. Particle size distribution parameters of a commercial albuterol MDI were measured using both Andersen (AI) and Marple-Miller (MMI) Cascade Impacters, where plates were either le ft uncoated or coated with silicone or glycerin. A previously validate d HPLC-EC method was used for the assay of albuterol collected by the impactor and in single spray content determinations. Results. Coating impactor collection plates had an impact on measured MMAD and GSD valu es for single puff measurements but very little or no effect for the m ulti puff measurements. Due to particle bounce, the percent of albuter ol fine particles deposited in the filter and impactor finer stages (< 1.10 mu m in AI and <1.25 mu m in MMI) in uncoated single puff experim ents was much higher in comparison to either coated single puff or mul ti-puff (coated and uncoated) measurements. Conclusions. Evaluation of drug load and plate coating are necessary to determine whether observ ed particle size distributions are representative of the generated aer osol or are the result of particle bounce and reentrainment. In order to minimize particle bounce, especially for. single puff determination s, it may be useful to apply a thin layer of a sticky coating agent to the surfaces of impactor plates.