无镇静作用的抗组胺药特非那定（ｔｅｒｆｅｎａｄｉｎｅ）能关闭心肌的钾离子通道并延长其动作电位，使心电图ＱＴ周期延长，导致室性心律不齐。而实际上在治疗剂量下使用特非那定时，经过肝脏的首过效应，它已被转化为对心脏没有毒害作用的非佐那定（ｆｅｘｏｆｅｎａｄｉｎ? The non-sedating antihistamine terfenadine turns off the potassium channel in the myocardium and prolongs its action potential, prolonging the QT cycle of the ECG, resulting in ventricular arrhythmias. In fact, at the therapeutic doses of terfenadine, it has been converted to fexofenadin, which is non-toxic to the heart, through the first-pass effect of the liver