The fluoroquinolones have two types of related adverse drug reactions (ADRs). Class effects, those affecting all fluoroquinolones to a variable degree have included (38): EGastro-intestinal intolerance, which occurs in around 4-5%. ECNS effects, common with those drugs that interact with either g-aminobutyric acid (GABA) or N-methyl-D-aspartate (NMDA) receptors in the brain, such as enoxacin, trovafloxacin, lomefloxacin and fleroxacin. Modern agents have low incidences of CNS effects, for example levofloxacin (< 1%). ESkin reactions, with rashes and itch occurring at rates of 0.5-5%, and an average of around 2%: the incidence with levofloxacin is exceptionally low at around 0.2%. EPhototoxicity, which is rare (< 0.05%) with modern compounds. EQTc prolongation, which occurs in about 3-5% of patients, usually amounting to no more than 3-6 msecs. It is rarely associated with either torsades de pointes or related sudden death. These events occur in < 1 per million treatment courses with drugs such as levofloxacin and moxifloxacin, and are less common than with, for example, macrolides such as erythromycin and clarithromycin. On the basis of animal and ex-vivo studies, some authorities believe some fluoroquinolones, including levofloxacin, to pose lesser risk in such circumstances (39). EFinally, tendinitis, which is a rare event occurring in < 0.02% of routine patients.

The second type is idiosyncratic reactions (38). Rare examples, usually with frequencies of < 0.05%, have occurred and appear to be specific to certain agents (which may be structurally related). These include severe phototoxicity, immunological reactions and related hepatitis, nephritis and hematological toxicity.