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 healthy volunteers using gamma scintigraphy. The radiolabel was delivered using a metered dose inhaler using a low vapour pressure chlorofluorocarbon fill (LVPA, 255 kPa) or a high vapour pressure chlorofluorocarbon fill (HVPA, 448 kPa) in a cross-over design trial. The data showed that a lower proportion of the dose (35%) was swallowed for HVPA compared with LVPA (49%). Within the lung, the proportion of the dose reaching the peripheral airways as determined by the penetration index was the same for both aerosols, although a greater pulmonary deposition of the dose was observed with HVPA. The results obtained confirm previous observations that greater than 40% of the marker achieves pulmonary deposition when dissolved in the propellant phase.