Labelling of ceftriaxone with (99m) Tc and its bio-evaluation as an infection imaging agent

Differentiation of bacterial and sterile inflammation will have a significant impact on the current clinical practice. Ceftriaxone (CTRX) was labelled with (99m) Tc and assessed for its ability to depict infection on scintigraphy. Stoichiometry was performed to optimize labelling parameters. Stability and bacterial binding was verified and biodistribution pattern was seen in normal, infected/inflamed animal models. (99m) Tc-CTRX prepared at pH 7 with stannous chloride of 50 µg, ligand of 30 mg, and boiling for 10 min gave labelling yield of 96.2 ± 0.2% with good stability. In vitro binding was higher for Escherichia coli than Staphylococcus aureus. Biodistribution in normal rats showed high uptake in hepatobiliary system, gut and urinary system. In animal models induced with infection or inflammation, lesion to normal ratios at 4 h were 2.36 ± 0.21, 12.66 ± 1.44 and 1.40 ± 0.01 with S. aureus infection, E. coli infection and turpentine oil inflammation, respectively. Infection specificity especially for E. coli was also confirmed on scintigraphic findings. Ceftriaxone can be labelled with (99m) Tc with high labelling yield at pH compatible with that of blood. Our preparation has shown stability in vitro and in human serum, and binds preferentially with bacteria. (99m) Tc-CTRX scintigraphy can be used to delineate sites of active infection and to differentiate infection and inflammation.