Light and Drugs: the photochemistry of fluoroquinolone antibiotics

Light-related adverse side-effects of drugs are now an important source of concern. In order
that the mechanism underlying to such effects is recognised, an in-depth photochemical study must be carried
out. The case of some fluoroquinolone antibiotics (norfloxacin, enoxacin, lomefloxacin) is discussed as
a representative example. These drugs undergo heterolytic fragmentation of the C—F bond leading to aryl
cations. Quantum yields in neutral water range from 0.001 to 0.5 depending on the charge transfer degree
of the ππ* state. Lower values are obtained at both acidic and basic pH. There is indication that the excited
state involved in most of this reactions is a relatively long-lived triplet. The aryl cations undergo intra- or
intermolecular reactions, and are presumably involved in the reported photo-toxic effect.