Drug interactions between Noroxin and Zithromax

MONITOR: Certain quinolones, including levofloxacin, norfloxacin, and ofloxacin, may cause dose-related prolongation of the QT interval in some patients. Coadministration with other agents that can prolong the QT interval may result in elevated risk of ventricular arrhythmias, including ventricular tachycardia and torsade de pointes, because of additive arrhythmogenic potential related to their effects on cardiac conduction. During postmarketing surveillance, rare cases of torsade de pointes and ventricular tachycardia have been reported in patients taking levofloxacin, norfloxacin, and ofloxacin. The levofloxacin cases primarily involved patients with underlying medical conditions or taking concomitant medications that may have been contributory. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). In addition, the extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s).

MANAGEMENT: Although the risk of a serious interaction is probably low, caution is recommended when levofloxacin, norfloxacin, or ofloxacin is administered concomitantly with drugs that prolong the QT interval, especially to patients with underlying risk factors. Since the magnitude of QTc prolongation increases with increasing plasma concentrations of the quinolone, recommended dosages and intravenous infusion rates should not be exceeded. Patients should be advised to seek medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, palpitations, or syncope.