Gallium-67 complexes as radioactive markers for assessment of gastric and colonic transit

Abstract

<h4>Unlabelled</h4>Constipation and gastroparesis are gastrointestinal tract disorders that can be assessed by using radioactive markers in conjunction with scintigraphic techniques. Indium-111-DTPA is the radiopharmaceutical of choice for treating colonic transit in constipated patients, but it is an expensive product and its availability has been unreliable. Indium-113m-DTPA was the tracer used in our study to determine the liquid gastric emptying rate in dual-isotope solid/liquid emptying studies, however, cessation of the 113Sn/113mIn generator production makes it unavailable. Thus, development of alternative tracers to 111In-DTPA and 113mIn-DTPA was essential.<h4>Methods</h4>Gallium-67-citrate and 67-Ga-EDTA were compared to 111In-DTPA to assess their efficacy for exclusive retention in the Gl tract. These markers were orally administered into rats and their three-day cumulative fecal excretion, urine excretion and carcass retention were measured. An in vitro gastric emptying model was used to determine liquid phase partitioning of 113mIn-DTPA, 67Ga-citrate and 67Ga-EDTA at 37 degrees.<h4>Results</h4>Gallium-67-citrate was predominantly excreted in the feces (97.2% +/- 0.2%) after three days, with negligible urine excretion (0.1% +/- 0.0%) and carcass retention (0.6% +/- 0.2%). These results are analogous to those obtained for 111In-DTPA for fecal excretion (96.7% +/- 2.6%), urine excretion (0.6% +/- 0.0%) and retention in the carcass (0.2% +/- 0.0%). Gallium-67-EDTA showed similar partitioning in the liquid phase of the gastric emptying model compared with 113mIn-DTPA.<h4>Conclusion</h4>Gallium-67-citrate is an economical and readily available alternative to 111In-DTPA as a colonic transit radiopharmaceutical. Gallium-67-EDTA is also an alternative to 113mIn-DTPA for assessing liquid-phase emptying in a dual-isotope solid/liquid gastric emptying study.