General factors influencing drug delivery to the lung.

The first devices to be developed for the delivery of bronchodilators and corticosteroids for the treatment of asthma were the pressurised metered dose inhalers (pMDIs). While pMDIs are viewed as patient friendly, they are associated with some serious disadvantages, such as considerable oropharyngeal deposition (due to the speed of delivery of the dose) and poor patient co-ordination of inhalation and activation. This has resulted in the development of alternative systems, such as the dry powder inhaler (DPI). However, DPIs also have problems, as there are difficulties in handling, measuring and metering fine particles. New devices, such as the Easi-breathe and Diskus inhalers, are now being introduced to overcome some of these problems. The ideal device is one that will produce a large proportion of respirable particles in the emitted dose. It must also deliver precise and uniform doses of drug to the patient. Further innovations are required to achieve these goals.