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Cordarone

Amiodarone belongs to a class of drugs called Vaughan-Williams Class III antiarrhythmic agent. It is used in the treatment of a wide range of cardiac tachyarhthmias, including both ventricular and supraventricular (atrial) arrhythmias. The chemical name for amiodarone is 2-butyl-3-benzofuranyl 4--3,5-diiodophenyl ketone hydrochloride. more...

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History

Amiodarone was initially developed in 1961 in Belgium as a treatment for angina. It was widely used throughout Europe as an anti-anginal medication, and was soon found to suppress arrhythmias.

Dr. Bramah Singh determined that amiodarone and sotalol belonged to a new class of antiarrhythmic agents (what would become the class III antiarrhythmic agents) that would prolong repolarization of the cardiac action potential. Based on this, the Argentinian physician Dr. Mauricio Rosenbaum began using amiodarone to treat his patients who suffered from supraventricular and ventricular arrhythmias, with impressive results. Based on papers written by Dr. Rosenbaum, physicians in the United States began prescribing amiodarone to their patients with potentially life-threatening arrhythmias in the late 1970s. By that time, amiodarone was commonly prescribed throughout Europe for the treatment of arrhythmias. Because amiodarone was not approved by the FDA for use in the United States at the time, physicians were forced to directly obtain amiodarone from pharmaceutical companies in Canada and Europe.

The FDA was reluctant to officially approve the use of amiodarone, since initial reports had shown increased incidence of serious pulmonary side-effects of the drug. In the mid 1980s, the European pharmaceutical companies began putting pressure on the FDA to approve amiodarone by threatening to cut the supply to the American physicians if it was not approved. In December of 1985, amiodarone was approved by the United States FDA for the treatment of arrhythmias. This makes amiodarone one of the few drugs approved by the FDA without rigorous randomized clinical trials.

Dosing

Amiodarone is available in oral and intravenous formulations. Orally, it is available under the trade names Pacerone^® (produced by Upsher-Smith Laboratories, Inc.) and Cordarone^® (produced by Wyeth-Ayerst Laboratories) in 200 mg and 400 mg tablets. It is also available in intravenous ampules and vials, typically in 150mg increments.

The dose of amiodarone administered is tailored to the individual and the dysrhythmia that is being treated. When administered orally, the bioavailability of amiodarone is quite variable. Absorption ranges from 22 to 95%, with better absorption when it is given with food.

Amiodarone is fat-soluble, and tends to concentrate in tissues including fat, muscle, liver, lungs, and skin. This confers a high volume of distribution (5000 liters in a 70kg adult) and a long half-life. Due to the long half-life of amiodarone, oral loading typically takes days to weeks.

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How should we manage newly diagnosed atrial fibrillation?
From Journal of Family Practice, 8/1/04 by Keith B. Holten

* What is the primary treatment goal of cardiac medication?

* What is the role of digoxin?

* When should medications be used to maintain sinus rhythm after cardioversion?

* Should all patients be anticoagulated with warfarin?

* What are the contraindications to warfarin therapy?

Recommendations for these management issues are found in the guideline developed in a joint effort of the American College of Physicians Clinical Efficacy Assessment Subcommittee and the American Academy of Family Physicians Commission on Clinical Policies and Research. It was funded by both organizations and approved by their Boards before publication. The target audience is internists and family physicians.

The target patients are adults with newly diagnosed atrial fibrillation. The guideline does not apply to postoperative patients, post-myocardial infarction patients, those with class IV heart failure or valvular heart disease, or patients taking antiarrhythmic medications.

The objective of this guideline is to recommend pharmacologic management of newly diagnosed atrial fibrillation. The evidence category for this guideline is management. Outcomes considered are control of heart rate and stroke risk reduction. The committees used the Guyatt method of grading recommendations, (1) a qualitative approach to the literature. These were revised to comply with the SORT taxonomy. (2)

* GUIDELINE RELEVANCE AND LIMITATIONS

Atrial fibrillation is common, affecting anywhere from 1% of the American population at age 60 to 8% at age 80. It is more common in men than women. Even if patients are asymptomatic, they are at increased risk of stroke (1.9%-18% per year).

A lengthy bibliography accompanies the guideline. Tables of supporting evidence are lacking, which makes it more difficult to analyze the final recommendations. The guideline is weakened by the lack of a cost-effectiveness analysis.

* GUIDELINE DEVELOPMENT AND EVIDENCE REVIEW

This guideline is based on background papers published by McNamara (3) and the John Hopkins Evidence-Based Practice Center (4) under contract with the Agency for Healthcare Research and Quality. There are 57 references.

The guideline group reviewed the evidence and made graded recommendations regarding rate control versus rhythm control, stroke prevention and anticoagulation, electrical conversion versus pharmacologic conversion, the role of transesophageal echocardiography in guiding therapy, and maintenance therapy.

* SOURCE FOR THIS GUIDELINE

Snow V, Weiss KB, LeFevre M, et al. Management of newly detected atrial fibrillation: A clinical practice guideline from the American Academy of Family Physicians and the American College of Physicians. Ann Intern Med 2003; 139: 1009-1017.

* OTHER GUIDELINES ON ATRIAL FIBRILLATION

* ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation. A report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines and Policy Conferences (Committee to Develop Guidelines for the Management of Patients with Atrial Fibrillation).

This 2001 guideline is the work of an international panel. Algorithms are provided for pharmacologic management of patients with newly diagnosed atrial fibrillation, pharmacologic management of patients with recurrent paroxysmal atrial fibrillation, antiarrythmic drug therapy to maintain sinus rhythm in patients with recurrent paroxysmal or persistent atrial fibrillation, and pharmacologic management of patients with recurrent persistent or permanent atrial fibrillation. Recent evidence regarding rate control versus rhythm control was not available at publication of this guideline.

Sources: American College of Cardiology, American Heart Association, European Society of Cardiology. ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation. J Am Coll Cardiol 2001, 38:1266i-1xx. (580 references) Fuster V, Ryden LE, Asinger RW, et al. ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation. A report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology. Eur Heart J 2001; 22:1852-1923. (580 references)

* Antithrombotic therapy in atrial fibrillation.

In: Sixth ACCP Consensus Conference on Antithrombotic Therapy.

This is an excellent review of a grading scheme for stroke risk and choice of anti-thromboric agents.

Source: Albers GW, Dalen JE, Laupacis A, et al. Antithrombotic therapy in atrial fibrillation. Chest 2001; 119(1 Suppl):194S-206S. (103 references)

* Atrial fibrillation: drug treatment and electric cardioversion.

This Finnish guideline makes recommendations regarding drug treatment, anticoagulation, and cardioversion for patients with atrial fibrillation and atrial flutter. The recommendations are not graded.

Source: Finnish Medical Society Duodecim. Atrial Fibrillation: Drug Treatment and Electric Cardioversion. Helsinki, Finland: Duodecim Medical Publications Ltd.; 2002 Mar 4. Various pages.

* Preventive health care, 2000 update. Use of ambulatory electrocardiography for the detection of paroxysmal atrial fibrillation in patients with stroke.

This guideline is from 2000 and found insufficient evidence to recommend for or against ambulatory electrocardiography to detect atrial fibrillation for patients after stroke or TIA.

Source: Bell C, Kapral M. Use of ambulatory electrocardiography for the detection of paroxysmal atrial fibrillation in patients with stroke. Canadian Task Force on Preventive Health Care. Can J Neurol Sc. 2000; 27:25-31. (78 references)

PRACTICE RECOMMENDATIONS

Grade A Recommendations

* Prescribe long-term warfarin at therapeutic levels unless stroke risk is low, as determined by risk factors: congestive heart failure, hypertension, age 75 years older, diabetes mellitus, or history of transient ischemic event/cerebrovascular accident. Warfarin should not be prescribed if there are contraindications of thrombocytopenia, recent trauma, surgery, or alcoholism.

* Atenolol (Tenormin), metoprolol (Lopressor, Toprol-XL), diltiazem, and verapamil are optimal choices for rate control during exercise and at rest. Digoxin (Lanoxin is a second-line agent and is only effective at rest.

Grade B Recommendations

* Rate control with anticoagulation is the primary goal of treatment. Consider rhythm control according to a patient's symptoms.

* Cardioversion by electrical conversion and pharmacologic conversion are both appropriate.

* For patients who elect cardioversion, options include 1) early antiocoagulation and cardioversion (with transesophageal echocardiography confirming absence of mural thrombus), or 2) delayed cardioversion with pre- and post-anticoagulation.

* Most patients who convert to sinus rhythm do not need maintenance rhythm therapy. When quality of life is threatened, the best agents are amiodarone (Cordarone), disopyramide (Norpace), propafenone (Rythmol), and sotalol (Betapace).

REFERENCES

(1.) Guyatt GH, Sackett DL, Sinclair JC, et al. User's guide to the medical literature:IX. A method for grading health care recommendations. JAMA 1995; 274:1800.

(2.) Ebell M, Siwek J, Weiss BD, et al. Strength of recommendation taxonomy (SORT): A patient-centered approach to grading evidence in the medical literature. Am Faro Physician 2004; 69:548-556.

(3.) McNamara RL, Tamariz LJ, Segal JB, Bass EB. Management of atrial fibrillation: review of the evidence for the role of pharmacologic therapy, electrical cardioversion, and echocardiography. Ann Int Med 2003;139:1018-1033.

(4.) McNamara RL, Bass EB, Miller MR, et al. Evidence report on the management of new onset atrial fibrillation. Agency for Healthcare Research and Quality publication no. AHRQ 01-E026. Rockville, MD: Agency for Healthcare Research and Quality; January 2001.

Correspondence: Keith B. Holten, MD, Clinton Memorial Hospital/University of Cincinnati Family Practice Residency, 825 W. Locust St., Wilmington, OH, 45177. E-mail: keholtenmd@cmhregional.com.

Keith B. Holten, MD

University of Cincinnati College of Medicine, Cincinnati, Ohio

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