Aerosol physiology, deposition, and metered dose inhalers.

The percentage of the dose reaching the lungs from a pressurized metered dose inhaler (MDI) is likely to be a major determinant of the efficacy of inhaled bronchodilators and corticosteroids. Yet MDIs may deposit no drug in the lungs in patients with poor inhaler technique and no more than 20% of the dose under optimum conditions. Spacer devices can help to deposit as much drug as from a correctly used MDI (even in patients with poor technique) but are often large and bulky. More compact (and easier to use) pressurized devices and multidose dry powder inhalers will be valuable additions to the range of apparatus available for asthma therapy and prophylaxis.