The Competition Between MDIs and DPIs

There has been an intensive effort to develop new ways to deliver aerosols. The DPI devices were developed for the following reasons: (1) They allow aerosol delivery without propellants, (2) they avoid the high velocity of MDI propellants, which leads to excess deposition in the oropharynx; and (3) they do not require the same hand-inspiratory muscle coordination needed for MDIs. Patient performance is still important with DPIs. Inspiratory flow must be properly maintained to achieve optimal performance. Lung deposition falls appreciably using a variety of devices when flow falls very much below the optimal rate of about 60L/min [55,56]. It is important to recognize that the recommended flowrate varies widely for different DPIs and that adherence to proper flow for each device is important. Acceptance of DPIs in the United States is well behind that in Europe.

There is a place for both of these devices. The deposition efficiency of both can be better than found in early studies of MDIs. Proper use of spacers improves the efficiency of MDIs, and proper inhalation flow is important for both devices. Comparative studies are legion [49,58-65], and sorting the confusing mass of information is difficult.

Young children have difficulties similar to older adults, namely, coordination between hand and inspiratory muscles while using MDIs. Devices have been developed to circumvent this problem. The dry powder inhaler only delivers into an air stream passing though the device as generated by the patient. Similarly, breath-actuated MDIs are made to respond to the beginning of patient inhalation. Some evidence suggests that for small children, the breath-actuated MDIs are easier to trigger than are DPIs [66].

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