In respiratory drug delivery, porous, lipid-based microparticles have shown performance advantages
over microcrystalline particles (Hirst et al., 2002). These engineered particles are manufactured by spray
drying of emulsions or suspensions. The purpose of this work is to combine an understanding of underlying
mechanisms with particle characterization data to develop models in support of a quality-by-design
(QbD) approach to drug development. Powders were manufactured using a laboratory scale spray dryer.
A thermodynamic model was developed for the spray drying process, allowing prediction of outlet temperature
and powder residual water content. A stochastic model based on a Monte-Carlo simulator was
developed to analyze the effects of relevant parameters on the aerodynamic size of the particles; modeled
results were verified by comparison to measured aerodynamic size distributions of spray-dried powders.
These modeling techniques allowed rank-ordering of the relative importance of formulation and process
variables, and aided in developing an understanding of the drying unit operation.