Drug interactions between arsenic trioxide and Pamelor

GENERALLY AVOID: Arsenic trioxide can cause QT interval prolongation and complete atrioventricular block. Theoretically, coadministration with other agents that can prolong the QT interval may increase the risk of ventricular arrhythmias, including ventricular tachycardia and torsade de pointes, because of additive arrhythmogenic potential related to their effects on cardiac conduction. During clinical studies involving 40 patients receiving arsenic trioxide for acute promyelocytic leukemia, 16 of them (40%) had at least one ECG tracing with a QTc interval greater than 500 msec. Prolongation of QTc was observed between 1 and 5 weeks after arsenic trioxide infusion and returned towards baseline by the end of 8 weeks. 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: If possible, medications that are known to prolong the QT interval should be discontinued prior to initiating therapy with arsenic trioxide and withheld for at least several weeks after completion of therapy. Caution is advised if concomitant use cannot be avoided. Patients should have frequent ECGs and be monitored for arrhythmias when QT interval is prolonged. An absolute QT interval exceeding 500 msec will require immediate action to correct concomitant risk factors, if any, as well as a thorough assessment of the need for continued therapy. Patients who develop syncope or arrhythmia should be hospitalized for clinical and laboratory monitoring. Arsenic trioxide should be temporarily discontinued until symptoms resolve, the QTc interval regresses to below 460 msec, and electrolyte abnormalities are corrected.