Effect of flow rate on coarse particle mass (CPM) from a dry powder inhaler (DPI) and a metered dose inhaler (MDI) / spacer delivering salbutamol

<bold>Objective:</bold> Spacers are regularly prescribed with MDI to help coordination and reduce oropharyngeal (OP) deposition caused by the aerosol velocity of the inhaler spray. DPIs require adequate inspiratory flow to aerosolize the powder and carry it past the OP. We undertook this study to determine if inspiratory effort could impart significant velocity to the powder particles that might lead to OP deposition. <bold>Methods:</bold> Easyhaler DPIs and Teva Salamol MDIs with AeroChamber2go* spacer were assessed by Next Generation Cascade Impactor at flow rates of 15 to 60 L/min. Salbutamol (model drug) was recovered quantitatively by HPLC. Results were expressed as mass >4.46µm (CPM), likely to deposit in the OP of a patient. Aerosol velocity measurements of DPI and MDI alone were made using high speed photography. <bold>Results:</bold> CPM (mean±sd) µg/actuation: <table-wrap><object-id>erj;64/suppl_68/PA2114/TB1</object-id><object-id>T1</object-id><object-id>TB1</object-id><table><colgroup><col></col><col></col><col></col><col></col></colgroup><tbody><tr><td><bold>Flow rate (L/min)</bold></td><td><bold>15</bold></td><td><bold>30</bold></td><td><bold>60</bold></td></tr><tr><td><bold>DPI_CPM</bold></td><td>65.9 +/- 3.1</td><td>55.1 +/- 5.6</td><td>51.8 +/- 6.1</td></tr><tr><td><bold>MDI/Spacer_CPM</bold></td><td>7.0 +/- 0.4</td><td>5.7 +/- 0.5</td><td>1.7 +/- 0.2</td></tr></tbody></table></table-wrap> Aerosol velocity measurements showed that the DPI plume was similar, if a little higher (6 vs 5 m/s) to the MDI without spacer. <bold>Conclusions:</bold> At all flow rates tested (sub optimal or optimal for powder dispersion) significant inertia was imparted to the DPI particles which would likely cause more than 50% of drug to impact in the OP. High speed photography comparisons at 10cm from the inhaler, representing the back of the throat, showed that DPI particle velocities were at least as high as MDI. This reinforces the recommendations to use a spacer with an MDI to reduce OP deposition (as shown in results) and minimize local and systemic side effects, an option not possible with the DPI.