Biodistribution and dosimetry of Tc-99m-ciprofloxacin, a promising agent for the diagnosis of bacterial infection

This study reports on the biodistribution and dosimetry of technetium-99m c iprofloxacin, a radioligand developed for the visualisation of bacterial in fection. Whole body scans were performed up to 24 h after intravenous injec tion of 370 MBq Tc-99m-ciprofloxacin in three male and three female volunte ers. Blood samples were taken at various times up to 24 h after injection. Urine was also collected up to 24 h after injection, allowing calculation o f renal clearance and interpretation of whole body clearance. Time-activity curves were generated for the thyroid, heart, liver and whole body by fitt ing the organ-specific geometric mean counts, obtained from regions of inte rest. The MIRD formulation was applied to calculate the absorbed radiation doses for various organs. The images showed rapid, predominantly urinary ex cretion of Tc-99m ciprofloxacin, with low to absent brain, lung and bone ma rrow uptake and low liver uptake and excretion. Accordingly, imaging condit ions are excellent for both the thoracic and the abdominal region, even at early time points (60 min) post injection. In none of the volunteers was th e gallbladder visualised. Approximately 60% of the injected activity was re covered in urine by 24 h post injection. The highest absorbed doses were re ceived by the urinary bladder wall, the thyroid, the upper large intestine, the lower large intestine and the uterus. The estimated mean effective dos e for the adult subject, taking into account the weight factors of the ICRP 60 publication, was 0.0083 mSv/MBq. The amount of Tc-99m ciprofloxacin requ ired for adequate planar and tomographic imaging results in an acceptable e ffective dose to the patient.