Poly(lactide-co-glycolide) microsphere formulations of darbepoetin alfa: Spray drying is an alternative to encapsulation by spray-freeze drying

Purpose. The purpose of this work was to evaluate spray-freeze drying and spray drying processes for encapsulation of darbepoetin alfa (NESP, Aranesp(R)). Methods. Darbepoetin alfa was encapsulated in poly(lactide-co-glycolide) by spray-freeze drying and by spray drying. Integrity was evaluated by size-exclusion chromatography and Western blot. Physical properties and in vitro release kinetics were characterized. Pharmacokinetics and pharmacodynamics were evaluated in nude rats. Results. Microspheres produced by spray drying were larger than those produced by spray-freeze drying (69 mum vs. 29 mum). Postencapsulation integrity was excellent for both processes, with <2% dimer by size-exclusion chromatography. In vitro release profiles were similar, with low burst (<25%) and low cumulative protein recovery at 4weeks (less than or equal to30%), after which time covalent dimer (less than or equal to6.5%) and high molecular weight aggregates (less than or equal to2.3%) were recovered by denaturing extraction. After a single injection, darbepoetin alfa was detected in serum through 4 weeks for all microsphere formulations tested in vivo, although relative bioavailability was higher for spray-freeze drying (28%) compared with spray drying (21%; p = 0.08) as were yields (73-82% vs. 34-57%, respectively). For both processes hemoglobin was elevated for 7 weeks, over twice as long as unencapsulated drug. Conclusions. Spray drying, conducted at pilot scale with commercial equipment, is comparable to spray-freeze drying for encapsulation of darbepoetin alfa.