Applying the AIM Concept in Support of Developing Improved In Vitro–In Vivo Relationships for OIPs - Good Cascade Impactor Practices, AIM and EDA for Orally Inhaled Products - page 376

Fig. 12.11 AIM-pHRT
system based on the ACI
equipped with “Alberta adult
throat” inlet ( Courtesy of
Copley Scientifi c Ltd, UK )
reference system, using MDI-delivered salbutamol as the test formulation [ 39 ]. All
CIs were equipped with a USP/Ph.Eur. induction port, as the purpose of this initial
validation exercise was to establish the measurement capability of the AIM-based
systems as cascade impactors, rather than compare the effect of different inlets. Full
details of the study are provided in Chap. 10 , so the summary of the main fi ndings
provided here just relates to the AIM-pHRT system. Importantly, this study con-
fi rmed that the measurement precision and accuracy for measures of FPM , CPM ,
and IM were comparable with that using the full-resolution ACI.
The follow-on study confi rmed that a fi lter soaked in the polyoxyethylene lauryl
ether surfactant (Brij 35) used to mitigate particle bounce from the collection plates
of these impactors was needed for the second stage of the AIM-pHRT impactor [ 40 ].
The surfactant-soaked fi lter provided additional protection from this source of bias in
order to obtain measures of EPM that were comparable with the range of values
obtained from the ACI. Although values of FPM and CPM were apparently unaf-
fected by particle bounce arising from displacement of the surfactant layer by the
incoming fl ow through the fi rst impaction stage, it may be prudent for the most accu-
rate work to consider the soaked fi lter option as a precaution with this type of AIM-
pHRT system. Recent work by Chambers and Smurthwaite, also discussed in Chap.
9 , with a fi ne particle dose-abbreviated impactor that is based on the parent ACVI
(Westech Instruments Ltd, UK), containing surfactant-soaked fi lters, indicates that
internal losses may be reduced with this mitigation measure for particle bounce [ 41 ].
A comparative study was undertaken in 2011, comparing an AIM-pHRT system
based on the C-FSA equipped with an adult AIT idealized throat inlet with the same
CI using the standard USP/Ph.Eur. induction port (Copley Scientifi c Ltd, UK,
Fig. 12.11 ).
MDI-delivered salbutamol (albuterol) was chosen as the OIP for evaluation,
given that the bulk of the API mass contained within the aerosol APSD is in the