Drug Interaction Report

MONITOR: Arsenic trioxide can cause QT interval prolongation and complete atrioventricular block. Theoretically, use of arsenic trioxide during intensive vitamin B12 therapy for the treatment of megaloblastic anemia may potentiate the risk of cardiac arrhythmias such as ventricular tachycardia and torsade de pointes because of the hypokalemia that may develop during the early phase of vitamin B12 therapy due to increasing potassium requirements as normal erythropoiesis is established. Hypokalemia is a known risk factor for ventricular arrhythmias associated with QT interval prolongation.

MANAGEMENT: Caution is advised when arsenic trioxide is administered to patients requiring vitamin B12 for severe megaloblastic anemia. Serum electrolytes should be evaluated and any abnormalities corrected prior to initiating therapy with arsenic trioxide. During therapy, potassium concentrations should be kept above 4 mEq/dL.

MONITOR: Ethanol may increase folic acid elimination and folic acid absorption is decreased in chronic alcoholics. Excessive alcohol consumption may lead to folate deficiency.

MANAGEMENT: Monitoring of patient response to folic acid supplementation if they also consume alcohol regularly may be recommended.

ADJUST DOSING INTERVAL: Concomitant administration of strontium with food or milk products may decrease its bioavailability by 60% to 70%.

MANAGEMENT: Strontium salts should be taken at least two hours before or two hours after food or milk products, and preferably at bedtime.