Light Obscuration to Monitor Aerosol Delivery from Dry Powder Inhalers
SARA MALONEY, Lynn Davis, Anthony Hickey,
RTI International Abstract Number: 280
Working Group: Instrumentation and Methods
AbstractMetrics of aerosol performance from dry powder inhalers (DPIs) are largely derived from in vitro cascade impaction and delivered dose uniformity analyses, giving rise to the aerodynamic particle size distribution (APSD) and emitted dose, respectively. However, from these metrics alone, a critical measurement is missing related to predicting in vivo performance. As aerosol release from a DPI is initiated by the inspiratory flow of the patient, the aerosol delivery rate (ADR) dictates where on the inspiratory flow the aerosol is delivered, and consequently, the regional lung deposition. The incorporation of a light obscuration window prior to aerosol entry to the cascade impactor allows for ADR to be monitored. A system was devised in which an LED light source (wavelength = 940 nm, intensity = 25 mW/sr, Kingbright) was directed to a near-IR mini-spectrometer (STS-NIR; Ocean Insight) across a sampling tube. The detector was connected to and operated by OceanView 2.0 software (Ocean Insight). Model powders of albuterol prepared through jet milling/lactose blending or spray drying were delivered from a #3 HPMC capsule using an RS-01 inhaler (Plastiape, Italy), and light obscuration data was collected to accompany cascade impaction data. Obscuration by the delivered powders while traveling through the sampling tube resulted in a decrease in absorbance measured by the mini-spectrometer. The absorbance profile gave rise to ADR metrics, including onset time, transit time, amplitude of response, and area under the response curve. Through the combination of the sampling apparatus and cascade impactor, both the ADR and APSD were simultaneously determined, and the influence of formulation characteristics on performance was established. Light obscuration as a complementary method for characterizing dry powder inhaler performance adds an additional in vitro metric that is also relevant for predicting in vivo performance.