Aerosols in the Health Care Field

:: Section 3

The pressurized MDI (pMDI) is the most commonly prescribed method of aerosol delivery in the United States. pMDIs are portable, compact, and relatively easy to use and the treatment time is short. A uniform dose of drug is dispensed within a fraction of a second after actuation, and the doses provided are reproducible throughout the canister life. pMDIs contain drug as microized powder, either dissolved or suspended in one or more chlorofluorocarbon (CFC) or hydrofluoroalkane (HFA) liquid propellants along with surfactants (oily, viscous, non-volatile substances used to keep the drug suspended in the propellants and to lubricate the valve mechanism). The volume of the formulation and the amount of drug released per actuation of the pMDI are a function of the size of the metering chamber. Its metering chamber volume can vary from 30 to 100 µL. Increasing the volume of the metering chamber decreases the rate of evaporation of the increased amount of propellant released. The result is increased loss of drug on the actuator mouthpiece. pMDIs are used to administer bronchodilators, anticholinergics, and steroids. More formulations of these drugs are available for use by MDI than for use with other nebulizers.