Pulmonary clearance rate of two chemically different forms of inhaled pertechnetate

Attempts to image the pulmonary deposition site of radiolabeled aerosols de livered by dry powder inhalers (DPIs) and pressurized metered-dose inhalers (pMDIs) using single photon emission computed tomography (SPECT) have been limited by the rapid pulmonary clearance of radiolabel. To determine wheth er aqueous solubility of the radiolabel is a significant factor, the pulmon ary clearance rates of two chemically different forms of Tc-99m were calcul ated. A dry powder formulation of terbutaline sulphate was radiolabeled for inhalation by Turbuhaler((R)) (AstraZeneca) using the water-soluble salt s odium pertechnetate and the water-insoluble salt tetraphenylarsonium pertec hnetate. A pilot study was conducted during which two control subjects each inhaled the two radiolabeled aerosols on separate days. Intrasubject clear ance rates for the two species were very similar. It was therefore conclude d that water insolubility of the pertechnetate salt alone was not enough to extend the lung residency time of the radiolabel.