Some Future Perspectives for Unit Dose Inhalation Aerosols

Abstract

Unit dose inhalation aerosols fail to achieve optimal lung deposition even though this can be achieved by dispersing 1-5 µm aerodynamic diameter particles in air. Dry powder generators require rapid inhalation for actuation and fail to deaggregate and release much of their powder charge because of high particulate adhesion forces. Conversely, pressurized metered dose inhalers (MDIs) fail because emergent propellant droplets are too large and travel too fast. The present unreliable dosimetry associated with the MDI stems from a desire to administer the whole of the metered dose. Rational design should concede on this point and concentrate on reducing primary droplet size and preventing emission of non-respirable large droplets. The loss of a constant proportion of each metered dose in the device and not the patient would be a major achievement. Improved inhalation dosimetry will facilitate future formulation developments designed to sustain local activity in the lung. This may be achieved by reducing particle dissolution rates in the airways.