Current Approaches to APSD Measurements of OIPs Based on Inertial Impaction - Good Cascade Impactor Practices, AIM and EDA for Orally Inhaled Products - page 42

Table 2.13 Suitability of the
cascade impactor method for
the various inhaler classes

Inhaler class Inhalation route Suitability
MDI Oral Good
DPI Good
SMI Good
Nebulizer Good
Nasal MDI Nasal a Fair
Aqueous nasal spray Poor
a Nasal inhaled products are shown to illustrate relatively
poor compatibility with the CI method but are outside
the scope of the topic

Table 2.14 Multistage CI apparatuses recognized in the European and United States
Pharmacopeias as of 2011

European
Pharmacopoeia Impactor or impinger US Pharmacopeia

Glass twin impinger (TI) Not referenced Apparatus A

Andersen eight-stage (ACI)
nonviable impactor without preseparator

Apparatus 1 for MDIs Apparatus D

Marple-Miller impactor model 160 Apparatus 2 for DPIs Not referenced

ACI with preseparator Apparatus 3 for DPIs Apparatus D

Multistage liquid impinger (MSLI) Apparatus 4 for DPIs Apparatus C

Next generation pharmaceutical
impactor (NGI)

Apparatus 5 for DPIs Apparatus E

Apparatus 6 for MDIs

The CI method is most suitable for the assessment of aerosols from MDI, DPI,
and SMI inhaler forms, although in the case of DPI testing, the compendial methods
require the impactor to be started from zero flow at the beginning of the sample,
simulating an inhalation maneuver, whereas it is evident from the previous sections
that CIs ideally operate at a fixed flow rate. Their applicability to the assessment of
nebulizing systems is slightly more problematic, in that precautions need to be
taken to prevent heat transfer from the CI to the aqueous aerosols that are produced
by these systems [ 48 ].
Likewise, precautions need to be taken with sprays from nasal MDIs, as these
frequently comprise aqueous solutions. Aqueous nasal spray characterization is
normally undertaken by laser diffractometry (LD), as the size range of the droplets,
which typically lies between 20 and 300 m diameters, is well outside the range of

operation of a CI [ 49 ]. This is the primary reason why this class of inhalers is largely
outside the scope of this publication. However, single-stage impactors with d 50 close
to 10

μ

m aerodynamic diameter have been used to identify the small subfraction of
ultrafine droplets potentially capable of penetrating the nasopharynx and entering
the airways of the lungs [ 50 ].
Chapter 601 of the US Pharmacopeia and the corresponding monograph 2.9.18
in the European Pharmacopoeia permit several different types of CI to be used for
OIP evaluations (Table 2.14 ).

μ