Respiratory clearance of aerosolized radioactive solutes of varying molecular weight

To determine the influence of varying molecular weight (mol wt) on respiratory clearance of aerosolized solutes, we studied eight radiopharmaceuticals, each administered to four dogs: sodium 99mTc pertechnetate (TcO4), 99mTc glucoheptonate ([99mTc]GH), 51Cr-ethylenedinitrotetraacetate ([51Cr]EDTA), 99mTc diethylenetriaminepentaacetate ([99mTc] DTPA), 111In diethylenetriaminepentaacetate ([111In]DTPA), 67Ga desferoxaminemesylate ([67Ga]DFOM), 99mTc dextran ([99mTc]DX) and 111In transferrin ([111In]TF). After aerosolization (0.8 m MMD, 2.4 GSD), clearance was determined for 30 min and then corrected by intravenous injection for nonairspace radioactivity. In-TF clearance (0.11 +/- 0.10%/min) was lower than TcO4 (6.32 +/- 0.62%/min), [99mTc]GH (1.50 +/- 0.37%/min), [51Cr]EDTA (2.38 +/- 1.02%/min), [99mTc]DTPA (3.51 +/- 0.40%/min), [111In]DTPA (2.35 +/- 0.42%/min), [67Ga] DFOM (1.99 +/- 0.49%/min) and [99mTc]DX (1.81 +/- 0.75%/min) clearances (p less than 0.001). TcO4 clearance was higher than others (p less than 0.001). Technetium binding to DX was unsatisfactory; aerosolization caused unbinding from DTPA. We conclude that respiratory clearance of large mol wt solutes within 30 min is negligible and, that clearance of molecules between 347-5,099 daltons differs greatly, suggesting that binding and/or intrapulmonary retention affect transfer.