Advantages of pressurized canister metered dose inhalers.

Metered dose inhalers (MDI) have provided a versatile, reliable, instantly available, self-contained, portable, low cost medical aerosol delivery system for more than 35 years. Currently, most of the drugs commonly used for treating reversible airflow obstruction due to asthma and chronic obstructive pulmonary disease (COPD) are available as MDI and consideration is being given to formulating other potentially useful drugs such as antibiotics, amiloride, and pentamidine in MDI. By means of particle size selective accessory devices, MDI can be used for pulmonary drug targeting which, by further improving the therapeutic ratio inherent to aerosol therapy, reduces local and systemic side effects and should allow application to the pulmonary airways of significantly larger doses of medication than could otherwise be administered safely. Appropriate masks and a variety of adapters have been developed to allow the MDI to be used in infants and children, as well as patients of all ages requiring assisted ventilation. While nebulizers and powder inhalers both have an important role to play in the management of airway and parenchymal disease, there is, as yet, no all-purpose aerosol generation and delivery system to replace the MDI. While the ideal is obviously to develop new environmentally friendly pressurizing liquid/gaseous systems that are chlorofluorocarbon free, this will take a minimum of a decade if, in the final analysis, it can be done at all. In the meantime, patients should be provided with the current formulations until appropriate substitutes become available.