Effect of inhalation profile and realistic throat geometry on aerodynamic performance characteristics of a developmental inhalation product delivered with the Genuair® inhaler

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Pharmacopoeial testing of inhalation products is suitable to detect changes in product performance but can hardly reflect performance during patient use. A method using realistic inhalation profiles and realistic throat models was developed, verified and applied to more accurately characterise a developmental inhalation product delivered with the Genuair® inhaler. 41 inhalation profiles were recorded and the 10th, 50th, and 90th percentiles were calculated for peak inspiratory flow rate (PIF; L/min), flow increase rate (FIR; L/s2) and inhalation volume (V; L). The three inhalation profiles closest to each of the percentiles for all three parameters were selected (weak, medium, strong). The USP/Ph.Eur. Induction Port (UIP), the Alberta Idealised Throat (AIT) as well as three anatomically accurate throats were used as throat models. The test setup included an inhaler in an air tight chamber connected to the respective throat and a mixing inlet, fixed between throat and pre-separator of a next generation impactor (NGI). A lung simulator was connected to the airflow between supplementary air and mixing inlet. This lung simulator was used to replay the inhalation profiles to reproduce them at the inhaler. During the study every throat was tested with each of the three profiles in a cross-over design in three replicates. Samples were assayed with a validated HPLC method. The results show that throat models and to a lesser extend the inhalation profiles have an impact on the fine particle dose (FPD), mass median aerodynamic diameter (MMAD), coarse fraction (CF) and throat deposition of the Genuair® inhalation product. Aerodynamic particle size distribution is influenced by different throat geometries rather than inhalation profiles. This test method can provide valuable information about inhalation products during development.