Protein powders for encapsulation: A comparison of spray-freeze drying and spray drying of darbepoetin alfa

Purpose. To evaluate spray-freeze drying and spray drying processes for fabricating micron- sized particles of darbepoetin alfa (NESP, Aranesp(R)) with uniform size distribution and retention of protein integrity, requirements for encapsulation. Methods. Darbepoetin alfa was spray-freeze dried using ultrasonic atomization at 120 kHz and 25 kHz and spray dried at bench-top and pilot scales. Reconstituted powders were evaluated by size exclusion chromatography and UV/VIS spectroscopy. Powder physical properties were also characterized. Results. Spray-freeze drying resulted in aggregation of darbepoetin alfa. Aggregates ( primarily insoluble) formed on drying and/or reconstitution. Particle size distributions were broad (span greater than or equal to 3.6) at both nozzle frequencies. Annealing before drying reduced aggregate levels slightly but increased particle size over 5-fold. Spray drying at inlet temperatures up to 135degreesC (and outlet temperatures up to 95degreesC) showed little impact on integrity. Integrity at bench-top and pilot scales was identical, with 0.2% dimer and no high molecular weight or insoluble aggregates detected. Particle size was small (less than or equal to 2.3 mum) with uniform distribution (span less than or equal to 1.4) at both process scales. Conclusions. Under the conditions tested spray drying, conducted at bench-top and pilot scales with commercially available equipment, was superior to spray-freeze drying for the fabrication of darbepoetin alfa particles for encapsulation.