Drug Interaction Report

ADJUST DOSING INTERVAL: Class III antiarrhythmic agents and ibutilide have additive effects and may prolong cardiac refractoriness and increase the risk of arrhythmias. Like other class III antiarrhythmic agents, ibutilide can cause dose-related QT interval prolongation. 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. 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: Class III antiarrhythmic agents should not be given concomitantly with ibutilide (which also has class III properties) or within four hours after ibutilide is given. In clinical trials, other class III antiarrhythmic agents were withheld for at least five half-lives prior to ibutilide infusion and for four hours after dosing, but thereafter were allowed at the doctor's discretion.

The recommended maximum number of medicines in the 'antiarrhythmics' category to be taken concurrently is usually one. Your list includes two medicines belonging to the 'antiarrhythmics' category:

• Bretylol (bretylium)
• ibutilide

Note: In certain circumstances, the benefits of taking this combination of drugs may outweigh any risks. Always consult your healthcare provider before making changes to your medications or dosage.

The recommended maximum number of medicines in the 'group III antiarrhythmics' category to be taken concurrently is usually one. Your list includes two medicines belonging to the 'group III antiarrhythmics' category:

• Bretylol (bretylium)
• ibutilide

Note: In certain circumstances, the benefits of taking this combination of drugs may outweigh any risks. Always consult your healthcare provider before making changes to your medications or dosage.