In-vitro characterisation of metered dose inhaler versus dry powder inhaler glucocorticoid products: influence of inspiratory flow rates.

PURPOSE To study the influence of inspiratory flow rate on the fine particle mass and the particle size distribution for metered dose inhaler (MDI) and dry powder inhaler (DPI) glucocorticoid products, in vitro. To compare the performance of MDI and DPI inhalers containing the same drug and strength at an impaction flow rate of 60 L/min. METHODS The Marple Miller cascade impactor model 150 and 160 were used to characterise several glucocorticoid MDI and DPI products at different simulated inspiratory flow rates (30 L/min, 60 L/min and 90 L/min). Following the actuation of one single inhaler puff the amount of drug deposited in each stage of the impactor was quantified using high performance liquid chromatography with UV detection at 242 nm. The size distribution of the primary particles of DPI products was measured by laser diffraction. RESULTS DPIs were significantly more dependent on impaction flow rate than MDIs. Except for Pulmicort(R), the fine particle mass FPM delivered from the MDI products was significantly higher than that delivered from the DPI aerosols. CONCLUSIONS Although the metered dose inhaler is the older technology it exhibits greater respirable dose in vitro than newer dry powder inhaler devices. Care should be taken when shifting from one inhaler dosage form to another because this may affect the actual dose delivered to the lung. Further in vivo studies may be warranted in light of these findings.