Pharmaceutical Manufacturing Handbook: Production and

700 AEROSOL DRUG DELIVERY
5.8.5.10 Dose Counters
A guidance document from the Food and Drug Administration (FDA) recommends
the addition of a dose counter to the MDI. This would overcome a long - standing
problem with the MDI, the inability of a patient to accurately know the number of
doses remaining in the canister [164] . Dose counters have been incorporated successfully
into multiple - dose DPIs. In general, the counter should give a clear indication
of when approaching end of life and the actual end of life. It should be either
numeric or color coded. If numeric, it should count downward and should be 100%
reliable and avoid undercounting [165] .
5.8.6
DRY POWDER INHALERS
5.8.6.1 Introduction
Dry power inhalers have been in use for over 40 years. They were developed as an
environmentally friendly alternative to the MDI. The early DPIs were simple in
design, portable, but again, a relatively ineffi cient means of delivering drugs to the
lungs for local action [166] . The Spinhaler, the fi rst DPI, has been prescribed in
Europe since the late 1960s. In general, the acceptance and use of DPIs is much
greater in Europe than in the United States. However, with the reformulation efforts
for MDIs, there are an increasing number of DPIs becoming available in the United
States (Figure 4 ).
Research and development for dry powder inhalers have two main focuses: the
optimization of the powder formulation for use in these inhalers and investigations
of novel DPI device designs and technology. An enormous literature now exists in
each of these areas; for more extensive reviews readers should consult refs. 33, 167,
or 168 .
FIGURE 4 Example DPIs available in United States.