Aerosol delivery device, categories

Before discussing the three categories of delivery device, the nature of the emitted aerosol will be considered. Droplet formation may be characterized in terms of the nature of the propulsive force and the liquid being dispersed, and this topic is dealt with for specific situations in the following sections. However, dry particles, which are delivered from suspension in pMDIs or from DPIs alone or from a blend, must be prepared in respirable sizes. The production of respirable aerosol particles has traditionally been achieved by micronization of the drug [25]. This... 

Unlike most other drug delivery systems, those in the respiratory area can have a major influence on physician/patient acceptance. A wide range of devices are available in the three main categories of dry powder inhalers (DPIs) and metered dose inhalers (MDIs), i.e., pressurised aerosols and nebulisers. The preferred type of inhaler varies considerably between countries (e.g., DPIs in Scandinavia and MDIs in the United States), and between patient groups (e.g., nebulisers for paediatrics). 

Powder inhalation devices are currently proving very popular, in spite of the fact that patients generally prefer metered dose aerosols. However, this preference is counterbalanced by the fact that compliance is much more difficult to achieve with aerosols. There is also a third category where the pack and the device are totally independent, e.g. a unit dose of nebuliser solution which is subsequently transferred to a pressurised or an ultrasonic nebuliser unit for delivery to the patient. 

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