The deposition of spray-dried beta-galactosidase from dry powder inhaler devices

The object of this study was to evaluate the in vitro deposition properties of a model spray-dried protein (beta-galactosidase) from a dry powder inhaler device (ISF inhaler). The stabilized spray-dried protein was evaluated alone and when blended with equal weights of (a) Avicel and (b) mannitol. The deposition properties were studied after exposure to environments of varying humidity using a twin impinger and a cascade impactor. The spray-dried material was extremely sensitive to humidity, with large reductions in respirable fraction occurring after storage at 43% relative humidity. The presence of a nonhygroscopic carrier (mannitol) did not prevent this reduction. There was no significant difference between the estimates of respirable fraction obtained using the cascade impactor and Min impinger for the material which had been stored in a dessicator. However, for the powders which had been exposed to environments of 43% relative humidity, the twin impinger was more reliable, as the cascade impactor results were adversely affected by entrainment of aggregates in the air stream.