Overview of Pulmonary Formulations and Delivery Systems

At present, dry powder inhalers (DPIs) are not used as commonly in the United States as are pMDIs. DPIs have been the last pharmaceutical inhalation aerosol system developed. Although the concept of operation is readily envisioned for these devices, the development of an efficient dry powder dispersion device intended for lung delivery has been notoriously difficult. Most of these devices function by using interactive mixtures of fine drug particles (1-5 pm diameter) and carrier excipient particles (usually 75 200 pm). Some evidence suggests that DPI performance is dictated largely by the physicochemical properties of the excipients used (5). However, as will be discussed, the availability of different choices of excipients is very limited, particularly in the United States. 

Nebulizers are designed primarily for the atomization of aqueous formulations either as solutions or suspensions, and typically contain additional excipients. These systems are nonpressurized formulations and do not contain propellants. Traditionally, nebulizers operated using one of two basic mechanisms jet nebulization or ultrasonic nebulization. Jet nebulizers (Fig. 3) function using the Venturi effect to 

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