Labeling and biological evaluation of 99m Tc-azithromycin for infective inflammation diagnosis

Azithromycin, an antibiotic used to treat bacterial infections, was labeled with 99m Tc. The maximum radiochemical yield of 99m Tc-azithromycin, 97.5 ± 0.9%, was attained under the following conditions: addition of 99m Tc to 2 mg of azithromycin in the presence of 50 μg of SnCl2·2H2O at pH 4, reaction time 30 min. 99m Tc-azithromycin complex was stable for 6 h. Biological distribution of 99m Tc-azithromycin was studied in mice infected with Staphylococcus aureus in the left thigh. The ratio of 99mTc-azithromycin uptake in the bacterially infected and contralateral thighs, T/NT, for was found to be 6.20 ± 0.12 at 2 h after intravenous injection (higher than the ratio obtained with the commercially available 99m Tc-ciprofloxacin), which was followed by gradual decline. The results obtained show that 99m Tc-azithromycin can be used for infection imaging and allows differentiation between bacterial infection and sterile inflammation.