Compatibility evaluation of metered-dose inhaler valve elastomers with tetrafluoroethane (P134a), a non-CFC propellant.

Compatibility of propellants, excipients, and solvents with the components of the valve greatly influences performance of metered-dose inhalers (MDIs). Ozone-friendly hydrofluoroalkane propellant 134a has potential for use as a chlorofluorocarbon (CFC) replacement. No suitable replacement for propellant 11 and 114 has yet been found and the problems arising from this may be overcome by use of ethanol as a solvent. In this study, compatibility of MDI valve elastomers Dowty Nitrile 0117, White Buna, and Type 674 (B) with P134a placebo formulations having different concentrations of ethanol was investigated. The results indicate that formulations containing no ethanol adversely affected the functioning of the valves. Higher concentrations of ethanol improved valve performance, but showed increased leakage. Physical characteristics of the valve elastomers evaluated by determining swelling caused after exposure to the P134a placebo formulations exhibited increased swelling with increasing concentrations of ethanol in the formulation.