Moisture uptake and its influence on pressurized metered-dose inhalers.

The objective of this study was to investigate moisture ingress into pressurized metered dose inhalers (pMDIs) containing hydrofluoroalkane (HFA) propellants and the consequences of this ingress. Moisture ingress into the pMDIs containing tetrafluoroethane (HFA 134a) or heptafluoropropane (HFA 227) was evaluated and modeled. The influence of water level in pMDIs on the stability of pMDIs containing triamicinolone acetonide (TAA) and beclomethasone dipropionate (BDP) in terms of particle growth, fine particle fraction, and drug solubility in the propellant system was evaluated using scanning electron microscopy, particle size analysis, single-stage impaction, and HPLC. The water level in HFA-containing pMDIs increased during storage and the process obeyed a diffusion model. HFA 134a had a greater tendency to take up moisture from the environment than did HFA 227. Unlike TAA, the propensity for particle growth of the suspended BDP in HFA propellants was significantly depressed by the increase in water level in the pMDIs. As a result, the fine particle fraction of the emitted BDP aerosols significantly increased as the water level in the HFA propellant was increased. Moisture ingress into pMDIs containing HFAs occurred during storage. The influence of the increased water level in pMDIs on the physical stability of the pMDI formulation and the dose delivery performance was a function of the composition of the internal lining of the container, the type of drug and propellant, and storage temperature.