Toxicity of quinolones

Reactions of the gastrointestinal tract, the CNS and the skin are the most often observed adverse effects during therapy with fluoroquinolones. At lea st for some of the newer fluoroquinolones a steep dose-response relationshi p of adverse effects seems to exist. Pathogenesis of the neurotoxic effects of fluoroquinolones is still unknown. Among the newer drugs, trovafloxacin caused mild CNS reactions such as dizziness and lightheadedness in a consi derable proportion of patients. Young females seem to be especially sensiti ve to this effect, which diminishes during treatment or if taken together w ith food. Cardiotoxic potentials of sparfloxacin and grepafloxacin are high er than those of other fluoroquinolones, but during therapy no clearcut dru g-related serious reactions have been reported, apart from a slight prolong ation of the QT interval. However, to avoid risks these drugs should not be prescribed to patients with known prolongation of the QT interval (e.g. pa tients on antiarrhythmics). Phototoxicity has been described for all quinolones, but derivatives with a halogen atom at position 8 show the highest potential for such reactions. Fleroxacin, sparfloxacin, clinafloxacin and lomefloxacin belong to this gro up of fluoroquinolones. The phototoxic potential of the other new fluoroqui nolones is considerably lower, but extensive exposure to UV light should ge nerally be avoided during therapy with all quinolones. Chondrotoxicity of quinolones, as observed in immature animals, can affect articular cartilage and/or the epiphyseal growth plate, depending on the de velopmental stage. Pathogenesis of chondrotoxicity can probably be explaine d by the magnesium-chelating properties of these drugs. As juveniles are es pecially sensitive, use of these drugs in paediatrics should be restricted to carefully selected indications (such as the use of ciprofloxacin in cyst ic fibrosis). Another manifestation of the toxic effects of quinolones on connective tiss ue structures are tendopathies. Tendinitis and tendon ruptures have occurre d as late as several months after quinolone treatment. Overall, quinolones are well tolerated drugs. Their specific toxic potentia ls have to be considered when they are chosen for treatment of bacterial in fections.