In the last decade, several third and fourth generation fluoroquinolones (FQs) have been approved for clinical
use. These new agents exhibit a more potent and broader-spectrum antibacterial activity and improved pharmacokinetic
properties in comparison to the earlier FQs. Although new FQs are generally safe and well tolerated, moderate-to-severe
toxicity events have been reported for some of them, leading to their restriction, suspension or even withdrawal from the
market. The most common FQ-related adverse effects (AEs) are usually mild and involve the gastrointestinal tract (e.g.
nausea and diarrhea) and the central nervous system (e.g. headache and dizziness). Uncommon, but severe AEs (e.g.
arthropathy, QTc interval prolongation, dysglycaemia and phototoxicity) and idiosyncratic reactions (e.g. hepatitis and
hemolytic anemia) have also been reported and will be discussed throughout this paper. The evidence currently available
suggests that AEs can be inherent to the FQ class or can be associated with a particular chemical moiety of the molecular
structure of each FQ, thus varying in frequency, severity and nature. The main goal of this review is to provide a
systematic evaluation of safety and tolerability data of the newer FQs with emphasis on those currently marketed.