Drug Interaction Report

MONITOR: Certain quinolones, including gemifloxacin, may cause dose-related prolongation of the QT interval in some patients. Theoretically, coadministration with other agents that can prolong the QT interval may result in additive effects and increased risk of ventricular arrhythmias including torsade de pointes and sudden death. No cardiovascular morbidity or mortality attributable to QTc prolongation occurred with gemifloxacin treatment in over 6775 patients during clinical trials, including 653 patients concurrently receiving drugs known to prolong the QTc interval and 5 patients with hypokalemia. The maximal change in QTc interval occurs approximately 5 to 10 hours following oral administration of gemifloxacin. 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 if gemifloxacin is used in combination with other drugs that can prolong the QT interval. Since the magnitude of QTc prolongation may increase with increasing plasma concentrations of gemifloxacin, the recommended dosage should not be exceeded, especially in patients with renal or hepatic impairment. Patients should be advised to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope.

GENERALLY AVOID: Concurrent use of ethanol and phenothiazines may result in additive CNS depression and psychomotor impairment. Also, ethanol may precipitate dystonic reactions in patients who are taking phenothiazines. The two drugs probably act on different sites in the brain, although the exact mechanism of the interaction is not known.

MANAGEMENT: Patients should be advised to avoid alcohol during phenothiazine therapy.