Enteric coating of micron-size drug particles through a Würster fluid-bed process

Enteric coated active pharmaceutical ingredient (API) particles can provide advantages in clinical and pre-clinical formulation development targeting intestinal drug release over traditional tablet and capsule formulations. The challenge with this approach is developing a robust coating process to achieve sufficient gastric protection and efficient intestinal release on micron sized particles. A Wurster coating fluid bed process to directly produce enteric coated API particles was developed at a 650 g scale and was scaled up to 20 kg. Generating API with low 3-dimensional aspect ratio structure was critical for this process and was achieved through a wet milling process. The starting particle size had D50 ~ 90 μm, and the D50 of the resulting coated particles could be as small as 180 μm. Scanning electron microscopy imaging and dissolution testing were used to characterize the properties of the enteric layer on the API particles as a function of coating thickness. Coated API particles achieved up to 8 h enteric protection in the gastric environment and rapid release in the intestinal environment.