Fluoroquinolones are widely used in human and in veterinary medicine due to their broad-spectrum antibacterial activity. They act by inhibiting type II DNA topoisomerases (gyrase and topoisomerase IV). Because of the sequence homology between prokaryotic and eukaryotic topoisomerases II, fluoroquinolones can pose a hazard to eukaryotic cells. However, published information concerning the genotoxic profiles of these drugs in vivo is sparse and inconsistent. We have assessed the activities of three fluoroquinolones, ciprofloxacin, enrofloxacin and norfloxacin, in the Drosophila melanogaster Somatic Mutation and Recombination Test (SMART) and measured their mutagenic and recombinagenic potentials. Norfloxacin was non-genotoxic. Ciprofloxacin and enrofloxacin induced significant increases in spot frequencies in trans-heterozygous flies. To test the roles of somatic recombination and mutation in the observed genotoxicity, balancer-heterozygous flies were also analyzed. Ciprofloxacin and enrofloxacin were preferential inducers of homologous recombination in proliferative cells, an event linked to loss of heterozygosity.
