Biopharmaceutical powders: particle formation and formulation considerations

It is well known that protein/peptide-based drug formulations are more stable in the solid state than in the liquid state, thereby offering stability advantages in ambient temperature storage, product shipping/distribution, and long-term shelf life. Novel powder-based drug delivery systems recently emerging for applications in sustained release, inhalation, intradermal delivery, etc, add more value to protein solid dosage forms. Despite great research interests in understanding the drying effects on protein stability and a large collection of publications focusing on this area, systematic accounts of powder formation techniques are lacking. This review is to summarize a number of methods currently available for protein powder preparation. Some are common methods such as lyophilization, spray drying, pulverization, and precipitation, and some methods are more recently developed such as supercritical fluid precipitation, spray-freeze drying, fluidized-bed spray coating and emulsion precipitation. In addition to examining the individual process effect on protein stability that is always the focus of formulation scientists, this review also likes to evaluate each method from a more practical sense in terms of process versatility and scalability. The conclusion is that each method has its own advantages and the use of a method is formulation and application specific. With the understanding of the principles and advantages of these methods, it can benefit our choice on selecting appropriate techniques for preparing a desired protein powder formulation for specific applications.