Optimizing drug delivery from metered-dose inhalers.

Metered-dose inhalers (MDIs) are being used with increasing frequency to administer medication used in the treatment of respiratory tract disorders. Inhaled medication is delivered directly to the tracheobronchial tree, allowing for a rapid and predictable onset of action. Studies show that only about ten percent of the dose from an MDI actually reaches the lung. The site of deposition within the lung is influenced by the aerosol characteristics, interpatient variability, and the technique by which the patient uses the inhaler. Spacer devices have been designed to overcome some of the problems encountered with MDIs and may be beneficial in certain groups of patients. The studies reviewed in this article suggest ways to alter the variables affecting inhalation in order to optimize drug delivery so that the patient will obtain the most benefit from the inhaled medication.