Biomedical Engineering Reference
In-Depth Information
Fig. 10.26
Total API recovery for eight different pMDI products comparing FPD-AVCI and non-
viable 8-stage ACI.
%LC
percent label claim (
From
[
33
]—
courtesy of W. Doub
)
In retrospect, the internal dead space associated with the FPD-AVCI is significantly
greater than that for the abbreviated nonviable ACI systems, due to the need to
accommodate the three dimensional structure of the Petri dish rather than near-to-
flat collection plates associated with the nonviable ACI internal configuration (com-
pare Fig.
10.28a, b
). The extra dead space in the FPD-AVCI might therefore be
expected to result in increased
FPF
<5.0μm
through increased time for particle shrink-
age due to cosolvent evaporation. However, this outcome was not seen to a marked
extent with formulations containing cosolvent except with Proventil™.
Furthermore, cosolvent evaporation would not explain the observed bias toward
larger values of
CPF
>5.0μm
, that was apparent with almost all the products, whether
or not cosolvent was present in the formulation. It therefore appears that another
explanation is needed to explain these results in a more satisfying way. One possi-
bility could be the potential for increased impaction of coarse particulate at the first
stage of the FPD-AVCI, again brought about by differences in internal geometry
between this abbreviated impactor and the nonviable ACI.
Further investigation is therefore warranted, this time, ideally using both AVCI
and nonviable ACI as control impactors, given the similarity of this impactor to the
interior of the FPD-AVCI (compare Fig.
10.16
with Fig.
10.28a
).
10.7
Assessing the Performance of AIM Systems
Based on the Fast Screening Impactor
Up until this section, the focus has been on abbreviated impactors that are based on
either the nonviable or viable ACI internal configurations. Such systems were the
first to be evaluated, as in the case of abbreviated nonviable ACI systems, they can be
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