Gallium-67 complexes as radioactive markers to assess gastric and colonic transit

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.

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.

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.

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.