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 mum) 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.