The most prominent adverse effects of the quinolones are nausea, vomiting, and diarrhea. Occasionally, headache, dizziness, seizures, insomnia, impaired liver function, and skin rashes have been observed as well as more serious reactions such as acute kidney injury, hypoglycemia (especially with gatifloxacin, which has been removed from the US market, and moxifloxacin), and anaphylaxis. With the exception of delafloxacin, all fluoroquinolones likely prolong the QT interval; it is unclear whether any one agent is implicated more than another. Quinolones should be used cautiously in patients with a history of prolonged QT or concomitant use of drugs known to prolong QT. Prolongation of the prothrombin time and the international normalized ratio has been observed in some patients receiving stable doses of warfarin after ciprofloxacin has been given, but this interaction is unpredictable and modest if it exists at all. Tendinitis and tendon rupture have been reported with quinolone agents. The proposed mechanisms for this adverse event are not completely understood. It is known that fluoroquinolones decrease type I collagen, elastin, fibronectin, and beta-1-integrin and inhibit cell proliferation and synthesis of matrix ground substance (fibroblast metabolism). However, the true mechanism for this complication is unclear. Nonetheless, risk factors are well known and include concomitant corticosteroid use, age older than 60 years, kidney dysfunction, and organ transplant. The FDA has required a black box warning for tendinopathy. Patients experiencing musculoskeletal symptoms while receiving fluoroquinolones should discontinue therapy. In addition, the FDA has issued warnings regarding peripheral neuropathy. Its onset can be within a few days of initiation of therapy and can be permanent in some patients. Lastly, while rare, fluoroquinolones are associated with an increased rate of aortic aneurysm and dissection, and the FDA recommends against use of fluoroquinolones in patients at high risk for these complications, including elderly patients and those with a history of high blood pressure, vessel blockages, and other genetic disorders.