Evaluating the depletion of enrofloxacin and ciprofloxacin in trout fish using zinc-65 radioisotope

The global emergence and spread of antimicrobial resistance (AMR) in human pathogens are mainly the consequence of antimicrobial use in human medicine and agricultural production systems. Therefore, using antimicrobials should be monitored effectively in the food production management systems. Developing standard veterinary drug residue monitoring programs is one part of such management systems and needs to be strengthened. Enrofloxacin is a third-generation synthetic fluoroquinolone antimicrobial agent used widely in the treatment of infections in humans and farm animals. Enrofloxacin and its metabolites (including ciprofloxacin) have been detected in many farmed fish products, highlighting the need for attention for fish products safety while controlling fish diseases. Herein, we implemented a new method for long-time measurement and visualization of enrofloxacin residues in trout fish using 65zinc radioisotope. Enrofloxacin was labeled with [65Zn] ZnCl2. The radiolabeled compound and non-labeled enrofloxacin were then administered simultaneously in the fish. Positron emission tomography (PET) scans were done at different intervals from 30 min to 35 days for visualization of the residues of enrofloxacin followed by precise measurement of the residues with a high purity germanium (HPGe) nuclear detector for labeled compounds and enzyme linked immunosorbent assay (ELISA) tests for non-labeled compounds. The results showed that depletion imaging and gamma spectroscopy of radiolabeled enrofloxacin and the metabolite in fish tissues are very precise, reliable and practical for exploring the biodistribution, metabolic and excretory profile as well as determination of Maximum Residue Limits (MRLs), withdrawal times (WDTs), and tracking of the drug residues.