The spray drying process is broadly applicable to a large number of APIs and formulation approaches. Multiple spray solvents
can be successfully used, simplifying the formulation of many drug and polymer combinations.
Figure 2: Overview of droplet-to-particle history.
Fundamental understanding of the spray drying process requires definition of a control volume to identify the key physical
situation. Mapping the process from droplet formation to particle formation, as shown in Figure 2, is critical to accurate
prediction of the impact of process variables on final particle attributes. By matching the conditions encountered during
the droplet-to-particle history, the critical-to-quality product attributes can be achieved, independent of process scale.
Figure 3: Process development flowchart.
A rational flowchart methodology based on this fundamental knowledge can be applied to optimize the spray drying process,
focusing on two core processes: atomization and drying (see Figure 3) (2).
Numerous atomization techniques can be employed to manufacture specific particles sizes for applications such as oral solubilization
(10 to 100 µm) and engineered particles for inhalation (1 to 5 µm). Engineering correlations are combined with an experimental
approach. Experiments are conducted to select target droplet-size distributions through changes in atomizer geometry and operating
conditions to achieve the target operating ranges and final particle size.
Drying conditions are selected based on physical-stability constraints and the desired morphology or density of particles.
Process parameters are correlated to particle attributes, serving as a basis for scale-up.
Use of engineering fundamentals in the spray drying process for amorphous dispersions allows understanding of key process
parameters and their impact on performance, manufacture, and stability. The process is easily scaled and is applicable to
with a wide variety of APIs.
1. D.T. Friesen et al., Mol. Pharm. 5 (6), 903–1144 (2008).
2. D.E. Dobry et al., J. Pharm. Innov.
4 (3), 133–142 (2009).