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Aerosols in the Health Care Field


:: Section 3

MDI (Metered Dose Inhaler)

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The most commonly prescribed method of aerosol delivery in the United States is the pressurized MDI (pMDI). There are several features of the pMDI that make it popular. The treatment time by using pMDIs is short. They are portable and relatively easy to use. With just a fraction of a second, a uniform dose of drug is dispensed after actuation, and reproducible doses are provided. pMDIs contain drug as microsized 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 metering chamber volume ranges from 30 to 100 µL and the metering chamber volume determines the volume of the formulation and the amount of drug released per actuation of the pMDI. However, increasing the volume of the metering chamber decreases the rate of evaporation. The resultant droplet size is bigger and therefore loss of drug on the actuator mouthpiece also increases. pMDIs are used to administer anticholinergics, bronchodilators, and steroids. More formulations of these drugs are available for use by MDIs than for use with other nebulizers.