amiodarone, Cordarone

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GENERIC NAME: amiodarone

BRAND NAME: Cordarone

DRUG CLASS AND MECHANISM: Amiodarone is an oral and injectable drug that is used to correct abnormal rhythms of the heart. (It is an antiarrhythmic medication.) Although amiodarone has many side effects, some of which are severe and potentially fatal, it has been successful in treating many arrhythmias when 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.

 Amiodarone was discovered in 1961 and approved by the FDA in December 1985.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets: 200 mg. Injection: 50 mg/ml

STORAGE: Tablets and injection should be kept at room temperature, 20-25 C (68-77 F).

PRESCRIBED FOR: Amiodarone is approved for recurrent ventricular fibrillation and hemodynamically unstable ventricular tachycardia.

DOSING: The recommended dosing schedule is an initial loading dose of 800-1600 mg daily for 1 to 3 weeks, followed by 600-800 mg daily for 1 month, then 400 mg daily for maintenance. Response should be closely monitored and dosing is individualized for each patient. Amiodarone may be administered once daily or given twice daily with meals to minimize stomach upset which is seen more frequently with higher doses.

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.




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