Limited pressure differential
results in only 20-40% efficiency
In the majority of commercially available devices,
the micronized drug (API) particles are generally
blended with larger carrier particles such as lactose.
The DPI must detach the pure drug from the carrier
during inhalation. In the majority of cases this is
achieved by impacting the carrier particles, typically
on an internal wall of the device, and the energy for
these impacts is provided by the inspiratory effort of
the patient. The energy available is therefore limited
by the negative pressure that the patient is able
to generate. Even if they could generate a perfect
vacuum, the 1 atmosphere of pressure differential still
may not be sufficient to fully detach and aerosolise
all of the API. Due to this inefficiency, typically only
20-40% of the pure drug detaches from the carrier
and is delivered to the lung. The majority of the pure
drug delivered from these devices (up to 80%) remains
attached to the larger carrier particles and impacts
in the mouth and throat, which is not only a waste of
drug but can lead to unpleasant side effects.