Spray drying is a technique used to produce dried powders
from a liquid feedstock containing a solid phase, often in solution
or suspension. The technique is well-suited to making dried
pharmaceutical powders, since particle characteristics such as size,
moisture content, flowability, and dispersibility may be influenced
by both the composition of the liquid feedstock and by the drying
process itself. In respiratory drug delivery applications, spray drying
is a particularly useful manufacturing technique as it enables
fine-tuning of the aerodynamic and bulk properties of the particles,
which can influence the efficiency of drug delivery to the lung and
the physical and chemical stability of the powders.
Porous, lipid-based microparticles have been shown to possess
properties well-suited for respiratory drug delivery (Hirst et al.,
2002). These particles are manufactured by spray drying of emulsions
or suspensions. The large number of formulation and process
variables involved in the manufacture of these engineered particles
makes the development of useful theoretical models a sound
investment from both a resource standpoint, as well as in support
of a QbD approach to drug product development.