A Cross-Industry Assessment Of The Flow Rate-Time Profiles Of Test Equipment Typically Used For Dry-Powder Inhaler (Dpi) Testing: Part 1-Compendial Apparatuses

We report a cross-industry study characterizing flow rate-time profiles of equipment used for testing dry-powder inhalers (DPIs). Nine organizations used the same thermal mass flow sensor to record flow rate-time profiles at the inlet of individual participant compendial DPI test systems including either sample collection tubes (SCT), the Andersen 8-stage non-viable impactor (ACI) or the Next Generation Impactor (NGI (TM)) with and without pre-separator (PS). The plan included some tests with a surrogate DPI consisting of one of three inlet orifices chosen to generate a 4-kPa pressure drop at each of the target final flow rates of 30, 60, and 90 l.min(-1), simulating the pressure drop typical of high-, medium-, and low-resistance DPIs. When a particular surrogate DPI was present at the inlet, rise times to 90% of these target flow rates (t(90)) were shortest at the highest target flow rate, and decreased linearly with decreasing apparatus internal volume, following the order: NGI-PS > NGI > ACI-PS > ACI > SCT. A flow acceleration parameter was also evaluated, expressed as the slope between the rise times when the flow rate attained 20% and 80% of each final steady flow rate (slope(t)(20/80)). Flow acceleration was smallest at the lowest target flow rate, decreasing exponentially with increasing internal volume. Measurements were also made without the surrogate DPI, providing a reference condition with no resistance at the inlet to the apparatus. These flow rate-rise time profiles will be useful for those involved in evaluating equipment for characterizing DPIs and in understanding the behavior of these inhalers in development or commercial production. Copyright (c) 2020 American Association for Aerosol Research