amiodarone

GENERIC NAME: amiodarone

BRAND NAME: Cordarone

DRUG CLASS AND MECHANISM: Amiodarone is used to correct abnormal rhythms of the heart. (It is an antiarrhythmic medication.) Amiodarone was discovered in 1961 and approved by the FDA in December of 1985. Although amiodarone has many side effects, some of which are severe and potentially fatal, it has been successful in treating many arrhythmias where other antiarrhythmic drugs have failed. Amiodarone is considered a "broad spectrum" antiarrhythmic medication, that is, it has multiple and complex effects on the electrical activity of the heart which is responsible for the heart's rhythm. Among its most important electrical effects are:

1. a delay in the rate at which the heart's electrical system "recharges" after the heart contracts (repolarization);
2. a prolongation in the electrical phase during which the heart's muscle cells are electrically stimulated (action potential);
3. a slowing of the speed of electrical conduction (how fast each individual impulse is conducted through the heart's electrical system);
4. a reduction in the rapidity of firing of the normal generator of electrical impulses in the heart (the heart's pacemaker);
5. a slowing of conduction through various specialized electrical pathways (called accessory pathways) which can be responsible for arrhythmias.

In addition to being an antiarrhythmic medication, amiodarone also causes blood vessels to dilate (enlarge). This effect can result in a drop in blood pressure. Because of this effect, it also may be of benefit in patients with congestive heart failure.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets (pink), round in shape: 200 mg.

STORAGE: Tablets should be kept at room temperature, less than 30°C (86°F).

PRESCRIBED FOR: Amiodarone is used for many serious arrhythmias of the heart including ventricular fibrillation, ventricular tachycardia, atrial fibrillation, and atrial flutter.

DOSING: Amiodarone usually is given in several daily doses to minimize stomach upset which is seen more frequently with higher doses. For this same reason, it is also recommended that amiodarone be taken with meals.

DRUG INTERACTIONS: Amiodarone may interact with beta-blockers such as atenolol (Tenormin), propranolol (Inderal), metoprolol (Lopressor), or certain calcium channel blockers, such as verapamil (Calan, Isoptin, Verelan, Covera-HS) or diltiazem (Cardizem, Dilacor, Tiazac), resulting in an excessively slow heart rate or a block in the conduction of the electrical impulse through the heart.

Amiodarone increases the blood levels of digoxin (Lanoxin) when the two drugs are given together. It is recommended that the dose of digoxin be cut by 50% when amiodarone therapy is started.

Flecainide (Tambocor) blood concentrations increase by more than 50% with amiodarone. Procainamide (Procan-SR, Pronestyl) and quinidine (Quinidex, Quinaglute) concentrations increase by 30%-50% during the first week of amiodarone therapy. Additive electrical effects occurs with these combinations, and worsening arrhythmias may occur as a result. Some experts recommend that the doses of these other drugs be reduced when amiodarone is started.

Amiodarone can result in phenytoin (Dilantin) toxicity because it causes a two- or three-fold increase in blood concentrations of phenytoin. Symptoms of phenytoin toxicity including unsteady eye movement (temporary and reversible), tiredness and unsteady gait.

Ritonavir (Norvir) can inhibit the enzyme that is responsible for the metabolism of amiodarone. Although no clinical problems have been recognized as a result of this interaction yet, it would be prudent to avoid this combination for fear of the potential for amiodarone toxicity.

Amiodarone also can interact with tricyclic antidepressants (for example, amitriptyline, Elavil), or phenothiazines (for example, chlorpromazine, Thorazine) and potentially cause serious arrhythmias.

Amiodarone interacts with warfarin (Coumadin) and increases the risk of bleeding. The bleeding can be serious or even fatal. This effect can occur as early as 4-6 days after the start of the combination of drugs or can be delayed by a few weeks.

Amiodarone can interact with some cholesterol-lowering medicines of the "statin" class, such as simvastatin (Zocor), atorvastatin (Lipitor), and lovastatin (Mevacor), increasing the risk of severe muscle breakdown and kidney failure or liver disease. This interaction is dose-related, meaning that lower doses of statins are safer than higher doses when used with amiodarone. An alternative statin, pravastatin (Pravachol), does not share this interaction and is safer in patients taking amiodarone.

Amiodarone inhibits the metabolism of dextromethorphan, the cough suppressant found in most over-the-counter (and some prescription) cough and cold medications (for example, Robitussin-DM). Although the significance of the interaction is unknown, these two drugs probably should not be taken together if possible.

Reference: FDA Prescribing Information