Influence of propellant composition on drug delivery from a pressurized metered-dose inhaler.

Hydrofluoroalkanes (HFAs) are used to replace chlorofluorocarbons (CFCs) as non-ozone-depleting propellants for pressurized metered-dose inhalers (pMDIs). HFA 134a and HFA 227 are used in combination to precisely manipulate the density and vapor pressure of pMDI formulations. The influence of propellant composition on the dose delivery characteristics of a suspension-based pMDI formulation was investigated. The results showed that as the density of the propellant blends approached the density of the suspended drug particles, the formulation became more physically stable and exhibited the most consistent dose delivery and greatest respirable fraction. The mass median aerodynamic diameter of the aerosolized particles contained in the emitted dose also was decreased by using propellant blends with higher vapor pressures. The performance of a suspension-based pMDI formulation was optimized by varying the propellant composition using HFA 134a and HFA 227.