WATER-VAPOR SORPTION STUDIES ON THE PHYSICAL STABILITY OF A SERIES OFSPRAY-DRIED PROTEIN SUGAR POWDERS FOR INHALATION/

One theory suggests that by maintaining the protein in an-amorphous gl assy sugar matrix, the physical hindrance encountered by the protein f unctions to stabilize it. Thus, the nature of the sugar/protein intera ction is important as is the maintenance of the sugar in an amorphous form without any recrystallization. Moisture is known to function as a plasticizer and facilitate crystallization and thus loss of the amorp hous state. We report the effect of cospray-drying with different prot eins on the physical stability of lactose and mannitol. Particle sizin g showed their suitability for inhalation, and the effect of exposure of the spray-dried products to moisture vapor was monitored gravimetri cally. Bovine liver catalase,bovine pancreatic insulin, and bovine pan creatic ribonuclease A when individually cospray-dried with lactose sh owed no extensive initial crystallinity by powder X-ray diffraction, b ut proteins cospray-dried with mannitol generally showed evidence of m annitol component crystallinity. Catalase appeared to inhibit lactose crystallization from an amorphous matrix to a greater extent than insu lin when exposed to short-term elevated humidity, but this difference was a kinetic feature. The hygroscopicities of the cospray-dried mater ials differed and indicated that each protein/sugar system required in dividual characterization to identify an optimal formulation.