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, sal butamol, with the radionuclide Tc-99m. The technique was used to prepa re metered-dose inhalers and dry powder inhalers for inhalation by six normal subjects and the deposition of drug within the lungs was measu red. In vitro data are presented from studies using an Andersen cascad e impactor which show that salbutamol and Tc-99m in the aerosol discha rged by the metered dose inhaler, or drawn through the instrument from a dry powder inhaler, have a closely matched particle size distributi on. Data from inhalers containing unlabelled salbutamol showed that th e addition of the radiolabel had not significantly altered its distrib ution. Using a dual headed gamma camera (Siemens Rota Camera), we stud ied 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 th e metered dose inhaler are considerably greater than those observed us ing indirect labelling techniques.