2020) A cross-industry assessment of the flow rate-time profiles of test equipment typically used for dry-powder inhaler (DPI) testing:

Abstract. The multi-stage cascade impactor (CI) is widely used to determine aerodynamic particle size distributions (APSDs) of orally inhaled products. Its size-fractionating capability depends primarily on the size of nozzles of each stage. Good Cascade Impactor Practice (GCIP) requires that these critical dimensions are linked to the accuracy of the APSD measurement based on the aerodynamic diameter size scale. Effective diameter (D eff ) is the critical dimension describing any nozzle array, as it is directly related to stage cut-point size (d 50 ). d 50 can in turn be determined by calibration using particles of known aerodynamic diameter, providing traceability to the international length standard. Movements in D eff within manufacturer tolerances for compendial CIs result in the worst case in shifts in d 50 of <±10%. Stage mensuration therefore provides satisfactory control of measurement accuracy. The accurate relationship of D eff to d 50 requires the CI system to be leak-free, which can be checked by sealing the apparatus at the entry to the induction port and isolating it from the vacuum source and measuring the rate of pressure rise before each use. Mensuration takes place on an infrequent basis compared with the typical interval between individual APSD determinations. Measurement of stage flow resistance (pressure drop; ΔP stage ) could enable the user to know that the CI stages are fit for use before every APSD measurement, by yielding an accurate measure of D eff . However, more data are needed to assess the effects of wear and blockage before this approach can be advocated as part of GCIP.

Compendial methods determining dry powder inhaler (DPI)-emitted aerosol aerodynamic particle size distribution (APSD) collect a 4-L air sample containing the aerosol bolus, where the flow, which propagates through the cascade impactor (CI) measurement system from the vacuum source, is used to actuate the inhaler. A previous article described outcomes with two CIs (Andersen eight-stage cascade impactor (ACI) and Next-Generation Pharmaceutical Impactor (NGI)) when the air sample volume was ≤4 L with moderate-resistance DPIs. This article extends that work, examining the hypothesis that DPI flow resistance may be a factor in determining outcomes. APSD measurements were made using the same CI systems with inhalers representing low and high flow resistance extremes (Cyclohaler® and HandiHaler® DPIs, respectively). The ratio of sample volume to internal dead space (normalized volume (V*)) was varied from 0.25 to 1.98 (NGI) and from 0.43 to 3.46 (ACI). Inhaler resistance was a contributing factor to the rate of bolus transfer; the higher resistance DPI completing bolus relocation to the NGI pre-separator via the inlet when V* was as small as 0.25, whereas only ca. 50% of the bolus mass was collected at this condition with the Cyclohaler® DPI. Size fractionation of the bolus from either DPI was completed within the ACI at smaller values of V* than within the NGI. Bolus transfer from the Cyclohaler® capsule and from the HandiHaler® to the ACI system were unaffected by the different flow rise time observed in the two different flow controller systems, and the effects the ACI-based on APSD measurements were marginal.

Multi-stage cascade impactors (CIs) are the preferred measurement technique for characterizing the aerodynamic particle size distribution of an inhalable aerosol. Stage mensuration is the recommended pharmacopeial method for monitoring CI "fitness for purpose" within a GxP environment. The Impactor Sub-Team of the European Pharmaceutical Aerosol Group has undertaken an inter-laboratory study to assess both the precision and accuracy of a range of makes and models of instruments currently used for optical inspection of impactor stages. Measurement of two Andersen 8-stage 'non-viable' cascade impactor "reference" stages that were representative of jet sizes for this instrument type (stages 2 and 7) confirmed that all instruments evaluated were capable of reproducible jet measurement, with the overall capability being within the current pharmacopeial stage specifications for both stages. In the assessment of absolute accuracy, small, but consistent differences (ca. 0.6% of the certified value) observed between 'dots' and 'spots' of a calibrated chromium-plated reticule were observed, most likely the result of treatment of partially lit pixels along the circumference of this calibration standard. Measurements of three certified ring gauges, the smallest having a nominal diameter of 1.0 mm, were consistent with the observation where treatment of partially illuminated pixels at the periphery of the projected image can result in undersizing. However, the bias was less than 1% of the certified diameter. The optical inspection instruments evaluated are fully capable of confirming cascade impactor suitability in accordance with pharmacopeial practice.

Soft contact lenses (SCLs) have recently been introduced as an alternative method for human tear protein sampling. However, SCLs are available in a variety of chemical compositions which affect protein binding specificity. Here we analyzed 8 different SCL materials to identify an optimal lens for tear protein sampling. Polymer contamination, mass spectrometry (MS) sample preparation method, total protein capture, individual protein specificity, and SCL cost were all assessed. Using a filter-aided sample prep (FASP) method with 4M guanidine for protein removal, only etafilcon A and verofilcon A did not have significant polymer contamination. Polymer was successfully removed using phosphate buffered saline (PBS) with S-Trap columns for all SCL materials, though yielding a slightly lower number of protein identifications per sample. Minor quantitative differences were observed between SCL materials. However, we also saw significant intersubject variation in protein abundance. Of all the assessed SCL materials, verofilcon A lenses yielded the most total protein while comfilcon A and senofilcon A had the least protein variability. As a newly released daily disposable modality (Precision 1, Alcon), verofilcon A has one of the longest predictable production schedules and one of the lowest costs per lens, making it beneficial for large-scale experiments and diagnostics. Furthermore, we demonstrate how protein binding bias with SCL tear sampling is useful for intra-experiment normalization. Overall, these experiments have led us to optimize our previous protocol for SCL tear protein sampling, highlighting important differences between SCL materials and identifying etafilcon A and verofilcon A as optimal materials for tear protein sampling.