In vitro clastogenicity of optical isomers of nadifloxacin.

The potential of optical isomers of the fluoroquinolone antibacterial agent nadifloxacin (NDFX, CAS 124858-35-1) to induce chromosomal aberrations in vitro was investigated in cultured Chinese hamster lung (CHL) cells for 24 h of continuous treatment. S- and R-enantiomers of NDFX showed significant differences in the results of the chromosomal aberration test, but no marked differences in the results of cytotoxicity test, i.e., S-NDFX induced chromosomal aberrations, but R-NDFX did not. These results were equivalent to those obtained with ofloxacin (OFLX, CAS 83380-47-6), which has a chemical structure similar to that of NDFX. Moreover, although neither NDFX nor OFLX induced aberrations, their mixtures, prepared from equal amounts of S- and R-enantiomers, did. This finding suggests that the racemic compound and the mixture of S- and R-enantiomers exist under different conditions within the solution.