Fluoroquinolones are generally well tolerated with most side effects being mild to moderate. Occasionally serious adverse effects occur.
Some of the serious adverse effects which occur more commonly with fluoroquinolones than with other antibiotic drug classes include CNS and tendon toxicity.
The currently marketed quinolones have safety profiles similar to that of other antimicrobial classes. Fluoroquinolones are sometimes associated with an QTc interval prolongation and cardiac arrhythmias, convulsions, tendon rupture, torsade de pointes and hypoglycemia.
These adverse reactions are a class effect of all quinolones, however, certain quinolones are more strongly associated with increased toxicity to certain organs. For example, moxifloxacin carries a higher risk of QTc prolongation, and gatofloxacin has been most frequently linked to disturbed blood sugar levels, although all quinolones carry these risks.
Some quinolones were withdrawn from the market because of these adverse events (for example, sparfloxacin was associated with phototoxicity and QTc prolongation, thrombocytopenia and nephritis were seen with tosufloxacin and hepatotoxicity with trovafloxacin).
Simultaneous use of corticosteroids is present in almost one-third of quinolone-associated tendon rupture.The risk of adverse events is further increased if the dosage is not properly adjusted, for example if there is renal insufficiency.
The serious events may occur during therapeutic use at therapeutic dose levels or with acute overdose. At therapeutic doses they include: central nervous system toxicity, cardiovascular toxicity, tendon / articular toxicity, and rarely hepatic toxicity.
Caution is required in patients with liver disease.Events that may occur in acute overdose are rare and include: renal failure and seizure.Susceptible groups of patients such as children and the elderly are at greater risk of adverse reactions during therapeutic use. Adverse reactions may manifest during, as well as after fluoroquinolone therapy has been completed.
Fluoroquinolones are considered high risk antibiotics for the development of C Difficile and MRSA infections. A previoualy rare strain of C Difficile which produces a more severe disease with increased levels of C Difficile toxins is becoming epidemic, may be connected to the use of fluoroquinolones.
Fluoroquinolones are more strongly associated with C difficile infections than other antibiotics including clindamycin, 3rd generation cephalosporins beta lactamase inhibitors. One study found that fluoroquinolones were responsible for 55% of C difficile infections.
The European Center for Disease Prevention and Control recommend that fluoroquinolones and the antibiotic clindamycin are avoided in clinical practice due to their high association with clostridium difficile, a potentially life-threatening super-infection.
The central nervous system is an important target for fluoroquinolone mediated neurotoxicity. Adverse event reporting in Italy by doctors showed fluoroquinolones among the top 3 prescribed drugs for causing adverse neurological and psychiatric adverse effects. These neuropsychiatric effects included tremor, confusion, anxiety, insomnia, agitation and in severe cases psychosis. Moxifloxacin came out worst amongst the quinolones for causing CNS toxicity.
Some support and patient advocacy groups refer to these adverse events as "fluoroquinolone toxicity". Some people from these groups claim to have suffered serious long term harm to their health from using fluoroquinolones. This has led to a class action lawsuit by people harmed by the use of fluoroquinolones as well as action by the consumer advocate group Public Citizen.
Partly as a result of the efforts of Public Citizen the FDA ordered a black box warnings on all fluoroquinolones advising consumers of the possible toxic effects of fluoroquinolones on tendons.
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