Prediction of the particle size distribution of the aerosol generated by a pressurized metered-dose inhaler

Abstract

Pressurized metered dose inhalers (pMDIs) are devices widely used for drug delivery in the respiratory tract. In this work, a mathematical model to predict the complete particle size distribution (PSD) of the aerosol generated by a pMDI is developed. The model combines the equations developed by Clark in 1999 that describe the flow within the inhaler, the Linear Instability Sheet Atomization (LISA) model and a method based on the Maximum Entropy Principle (MEP). Mathematically it is found that the PSD can be represented by a lognormal function with geometric standard deviation equal to 1.56. The model does not contain fitting parameters and is validated with experimental information for a formulation containing salbutamol and HFA-134a as drug and propellant, respectively. Simulations are performed to explore how the propellants HFA-134a and HFA-227ea affect the PSD of the aerosol generated by the inhaler.