THE PHYSICOCHEMICAL BASIS OF RADIOLABELING METERED-DOSE INHALERS WITHTC-99M

Over the past decade, a number of different approaches have been propo sed for the radiolabelling of metered dose inhalers (MDIs) in order to permit gamma scintigraphic imaging of emitted aerosols following inha led administration. More recently, methods have been described for the indirect Tc-99m-labelling of drugs incorporated into commercial MDI p roducts. This paper attempts to rationalise such methods from a surfac e chemical perspective in order to: 1) elucidate the mechanism of asso ciation of the radiolabel and drug; 2) predict the appropriateness of the techniques to all MDI products and; 3) propose in vitro testing me thods to validate the labelling efficiency prior to in vivo evaluation .