This paper focuses on the development of four major adverse drug reactions (ADRs) associated with some fluoroquinolones: convulsions, phototoxicity, cardiac effects, and hepatotoxicity. CNS adverse events have been linked to fluoroquinolone administration, including seizures, which are more likely with co-administration of NSAIDs. Only 61 cases of convulsions have been reported with levofloxacin, with 33 of those affected having received NSAIDs. The assumed rate of serious convulsions was as low as 1/65,000 with NSAIDs and 1/260,000 without NSAIDs. Levofloxacin has a very low phototoxicity-inducing potential confirmed by pre-clinical animal studies and the results of post-marketing surveillance (PMS). Pre-clinical results demonstrated that levofloxacin was 20 times less phototoxic than sparfloxacin and PMS data show that serious phototoxicity develops in only 1 in 1.8 million cases treated with levofloxacin. While many fluoroquinolones are associated with cardiac effects, pre-clinical data has shown that compared with sparfloxacin and grepafloxacin, levofloxacin has no effect on myocardial conduction. PMS data further support the safety of levofloxacin in this regard. While trovafloxacin is associated with serious hepatic problems, PMS data demonstrates that levofloxacin has a very low incidence of 1/100,000 hepatic effects. These results were confirmed in a prospective study that confirmed a low 1.3% incidence rate for all ADRs associated with levofloxacin. Copyright 2001 S. Karger AG, Basel