Antiarrhythmic drugs with warfarin

Is the drug likely to he co-prescribed with a drug of narrow therapeutic index For example, a drug for angina, cardiac failure or an antiarrhythmic agent is likely to be co-prescribed with warfarin. If there is any evidence of enzyme induction or inhibition, a clinical study with warfarin may be required. 

With warfarin, one is always concerned about pharmacodynamic and pharmacokinetic drug interactions. None of the antiarrhythmic drugs mentioned above are likely to cause a pharmacodynamic interaction with warfarin. However, amiodarone is a cytochrome P450 enzyme inhibitor and increases warfarin s antithrombotic effects. Patients taking both drugs usually need to decrease their dose of warfarin. 

Patients with chronic atrial fibrillation—a common supraventricular arrhythmia—routinely receive warfarin to prevent the development of blood clots in the poorly contracting atrium and to decrease the risk of embolism of such clots to the brain or other tissues. Such patients are also often treated with anti arrhythmic drugs. The primary goals of antiarrhythmic treatment are to slow the atrial rate and, most importantly, control the ventricular rate. 

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