The influence of flow rate on the aerosol deposition profile and electrostatic charge of single and combination metered dose inhalers

Purpose. The capability of the electrostatic next generation impactor (eNGI) has been investigated as a tool capable of measuring the electrostatic charge of single (Flixotide™; containing fluticasone propionate (FP)) and combination (Seretide™; FP and salmeterol xinafoate (SX)) pressurised metered dose inhalers (pMDIs) at different flow rates. Methods. Aerosol mass distributions were investigated at 30, 60 and 90 l.min−1 and simultaneous charge measurements recorded. Results. Analysis of the mass distribution data indicated a flow dependent relationship, where the aerosol performance (aerodynamic diameter <5 μm) of FP significantly increased between 30 l.min−1 and 60 l.min−1 for both formulations. No significant increase in SX was observed for Seretide with increased flow rate. Analysis of the charge distribution indicated both formulations to primarily charge negatively with a concurrent increase in charge with increased flow rate. Interestingly, the charge-tomass ratio remained relatively constant between 30 l.min−1 and 60 l.min−1 and increased at 90 l.min−1, indicating that charging was majorly influenced at the highest flow rate. Conclusions. This study has shown how the eNGI could be used as a simple Pharmacopeia based methodology for the evaluation of mass and charge profiles of single and combination pMDIs at a series of flow rates.