Aiming for a moving target: challenges with impactor measurements of MDI aerosols

International Journal of Pharmaceutics
Stephen W Stein

Abstract

Experiments were conducted to illustrate some of the challenges associated with measuring dynamic MDI aerosols. Experimental HFA-134a solution MDIs containing 8 or 20% ethanol were measured using the Andersen cascade impactor using three different inlets. It was demonstrated that the size distribution of MDI aerosols changes substantially during the measurement process. The measured size distribution was shown to be dependent on the degree of evaporation that has occurred prior to size measurement. Additionally, the degree of evaporation prior to measurement also influences the number of modes present in the measured size distribution. While MDI aerosols appeared to have a separate large particle mode when measured using the U.S. Pharmacopeial induction port ("USP inlet"; [U.S. Pharmacopeia, 1996. Physical tests and determinations <601> aerosols, metered dose inhalers, and dry powders. Pharmacopeial Forum 22, pp. 3065-3095]), the aerosols were shown to be monomodal when measured using a large volume inlet. The apparent large particle mode observed with the USP inlet seem rather to be droplets from the same monomodal distribution that have not fully evaporated. The complex interaction of the MDI plume and inlet configuration was...Continue Reading

Citations

Aug 29, 2013·BioMed Research International·Imran Y Saleem, Hugh D C Smyth
Dec 23, 2010·Expert Opinion on Drug Delivery·Remigius U Agu, Michael I Ugwoke
Dec 17, 2014·Expert Opinion on Drug Delivery·James W IveyWarren H Finlay
May 24, 2016·International Journal of Pharmaceutics·D A LewisP M Young
Nov 11, 2017·Therapeutic Delivery·Allen E HaddrellJonathan P Reid
Feb 19, 2016·Pharmaceutical Research·Nicholas Mason-SmithDamon Honnery
Jun 8, 2019·International Journal of Pharmaceutics·Daniel J DukeDamon Honnery

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