THE LUNG DEPOSITION OF SALBUTAMOL, DIRECTLY LABELED WITH TC-99M, DELIVERED BY PRESSURIZED METERED-DOSE AND DRY POWDER INHALERS

A method is described for the radiolabelling of the beta2-agonist, salbutamol, with the radionuclide Tc-99m. The technique was used to prepare metered-dose inhalers and dry powder inhalers for inhalation by six normal subjects and the deposition of drug within the lungs was measured. In vitro data are presented from studies using an Andersen cascade impactor which show that salbutamol and Tc-99m in the aerosol discharged by the metered dose inhaler, or drawn through the instrument from a dry powder inhaler, have a closely matched particle size distribution. Data from inhalers containing unlabelled salbutamol showed that the addition of the radiolabel had not significantly altered its distribution. Using a dual headed gamma camera (Siemens Rota Camera), we studied six normal volunteers and measured a mean (+/-SD) lung deposition of 11.3 (2.2)% of the dose discharged from a dry powder inhaler and 24.1 (8.5)% from the metered dose inhaler. The deposition values from the metered dose inhaler are considerably greater than those observed using indirect labelling techniques.