EFFECT OF FORMULATION FACTORS ON THE OBSERVED BOUNCE IN CASCADE IMPACTORS USED TO MEASURE THE SPRAY PARTICLE-SIZE OF METERED-DOSE INHALERS

This study was conducted to investigate the extent of particle reentra inment, or bounce, in cascade impactors used to measure the size of th e spray from single and multiple doses of metered dose inhalers (MDIs) , and to determine the effect of some common formulation properties on the observed bounce. MDIs were formulated as suspensions or solutions , with varying levels of surfactant. These were fired into two impacto rs (the Andersen Sampler Mark II and the Marple-Miller model 150), the collection surfaces of which were uncoated or coated with silicone oi l or glycerin, The amount of drug from a formulation collected on each stage was determined and comparison was made between results with coa ted and uncoated stages. Efficacy of the coating for eliminating bounc e was demonstrated by comparing single shots with multiple shots. Diff erent ways of describing bounce effects offer varying indications of i ts significance. The suspension formulations (containing surfactant) a ll showed evidence of bounce, but solution formulations showed little or none. Silicone oil and glycerin were equally effective in eliminati ng bounce. Results with impactors of two different designs were simila r. Particle bounce was shown to occur with a variety of formulations w hen impactor stages are not coated. (C) 1998 Elsevier Science B.V. All rights reserved.