Drug Interactions between dofetilide and iohexol

MONITOR: The use of iodine-containing contrast media for coronary angiography in patients treated with certain antiarrhythmics such as amiodarone may result in significant prolongation of the QT interval. These contrast agents can be arrhythmogenic when injected into the coronary arteries and may have additive effects on cardiac repolarization when coadministered with antiarrhythmic agents that prolong the QT interval. In a retrospective study of patients who underwent cardiac catheterization at a German hospital, 21 patients who had been receiving long-term amiodarone therapy exhibited significantly increased QT interval 12 to 24 hours after catheterization compared to 21 age-matched controls who received cardiac catheterization without prior amiodarone or other QT prolonging treatment. In the amiodarone group, the QTc interval (i.e., QT interval corrected for heart rate) increased on average by 10% from 433 ms to 480 ms. QTc prolongation exceeding 500 ms did not occur in any of the amiodarone patients before catheterization but occurred in 6 patients after catheterization. No significant change was observed in the control group.

MANAGEMENT: Caution is advised if iodine-containing contrast media are used for coronary angiography in patients treated with class IA (e.g., disopyramide, quinidine, procainamide) or class III (e.g., amiodarone, dofetilide, ibutilide, sotalol) antiarrhythmic agents. Increased surveillance and ECG monitoring may be appropriate. Patients who receive outpatient angiographies should be advised to seek medical attention if they experience symptoms that could indicate the occurrence of arrhythmia such as dizziness, palpitations, or syncope.