EFFECT OF VAPOR-PRESSURE ON THE DEPOSITION PATTERN FROM SOLUTION-PHASE METERED-DOSE INHALERS

The pulmonary deposition of Tc-99m-labelled hexamethyl propylene amine oxime, used as a model for propellant soluble drugs, was studied in h ealthy volunteers using gamma scintigraphy. The radiolabel was deliver ed using a metered dose inhaler using a low vapour pressure chlorofluo rocarbon fill (LVPA, 255 kPa) or a high vapour pressure chlorofluoroca rbon fill (HVPA, 448 kPa) in a cross-over design trial. The data showe d that a lower proportion of the dose (35%) was swallowed for HVPA com pared with LVPA (49%). Within the lung, the proportion of the dose rea ching the peripheral airways as determined by the penetration index wa s the same for both aerosols, although a greater pulmonary deposition of the dose was observed with HVPA. The results obtained confirm previ ous observations that greater than 40% of the marker achieves pulmonar y deposition when dissolved in the propellant phase.