Fluoroquinolones 是感染症常用的抗生素，其產生QT 間隔延長的結果可能會造成致命的心律不整，即torsade de pointes (TdP)。依據體外試驗的結果，其作用機轉主要與阻斷心臟電壓控管的鉀離子通道相關，潛在風險較高者為sparfloxacin、grepafloxacin 及gatifloxacin，moxifloxacin 居中，levofloxacin 與ciprofloxacin 較低，ofloxacin 最低。一般來說，在其他危險因子存在時，fluoroquinolones 更容易造成心室電位不穩定並引發TdP，危險因子如女性、年齡、家族性長QT 症候群、病人本身校正QT 間隔大於500 ms、心臟疾病、心律異常、電解質異常、藥物劑量過高、合併使用其他會導致QT 間隔延長的藥品。瞭解如何適時採取預防措施，以降低心毒性的發生，是醫療人員的重要課題。

Fluoroquinolones are commonly prescribed antibiotics, but the side effect of prolonged QT interval in electrocardiograms may lead to torsade de pointes (TdP), a life-threatening cardiac arrhythmia. The prolonged QT intervals were mainly caused by blockage of voltage-gated potassium channels in the myocardial cells. Fluoroquinolones differ in their potency in extending QT intervals as following: sparfloxacin, grepafloxacin, gatifloxacin > moxifloxacin > levofloxacin, ciprofloxacin > ofloxacin. In general, fluoroquinolones may induce electrical instability within the ventricle and, when other risk factors exist, potentiate the occurrence of TdP. Commonly known risk factors are female, age, familial long QT syndrome, heartrate-corrected QT interval (QTc) over 500 ms, heart disease, cardiac arrhythmia, electrolyte abnormality, excessive dosing, combined with other medicines associated with prolonged QT interval. Awareness of the risk factors and timely action to reduce adverse cardiac toxicity is an important issue for healthcare providers.