Drug deposition of pressurized inhalation aerosols.

When a pressurized inhalation aerosol is used, a high loss of drug substance occurs in the upper respiratory tract. This is explained by the rather slow propellant evaporation after the initial aerosol generation, and by the high initial aerosol velocity. Indirect measurements can be performed with a view to obtaining an indication of the deposition pattern in subjects; but a radioactive technique must be used in order to obtain the complete deposition pattern in the body. The drug loss occurring when a person exhales seems to be low compared to the dose entering a subject.