Drug Targeting Organ-Specific Strategies

66 3 Pulmonary Drug Delivery: Delivery To and Through the Lung
• Dosing system.
• Disintegration principle. In general, the powders in the inhaler are not formulated as single
particles, but as adhesive mixtures or spherical pellets (Figure 3.3). These mixtures or
pellets are suitable for processing and metering. However, the particle size of these mixtures
or pellets is far too large for lung deposition. Therefore, the pellet or mixture has to
be disintegrated to make an aerosol cloud with the desired particle size (< 5 µm). Many
different disintegration principles exist. They may vary from a simple screen (Rotahaler)
to twisted powder channels (Turbuhaler) or a cyclone chamber as used in de
Novolizer [54].
• A mouthpiece. The mouthpiece may be used to control the direction of the aerosol cloud
in the mouth and throat, in order to reduce drug deposition in the oropharyngeal cavities.
De Boer et al. [55] use a so-called sheath flow to reduce mouth deposition.
Figure 3.3. Scanning electron microscopy images of spherical pellets of budesonide (upper photograph)
and of an adhesive mixture of lactose and micronized salbutamol (lower photograph).