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). 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 microm vs. 29 microm). 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 4 weeks (< or = 30%), after which time covalent dimer (< or = 6.5%) and high molecular weight aggregates (< or = 2.3%) 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.