|
Actual product may differ in appearance from image shown.
GENERIC NAME: amiodarone
BRAND NAME: Cordarone (Origin: UK)
DRUG CLASS AND MECHANISM: Amiodarone is used to correct abnormal rhythms of the heart (an antiarrhythmic medication). Amiodarone was discovered in 1961. Amiodarone was approved by the FDA for clinical use as an antiarrhythmic agent 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 antiarrhythmics fail. 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:
- a delay in the rate at which the heart's electrical system "recharges" after the heart contracts (repolarization);
- a prolongation in the electrical phase during which the heart's muscle cells are electrically stimulated (action potential);
- a slowing of the speed of electrical conduction (how fast each individual impulse is conducted through the heart's electrical system);
- a reduction in the rapidity of firing of the normal generator of electrical impulses in the heart (the heart's pacemaker);
- 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.
PREPARATIONS: Tablets (pink), round in shape: 200mg.
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 is 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 (e.g. amitriptyline, Elavil), or phenothiazines (e.g. 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 inhibits the metabolism of dextromethorphan, the cough suppressant found in most over-the-counter (and some prescription) cough and cold medications (e.g. Robitussin-DM). Although the significance of the interaction is unknown, these two drugs probably should not be taken together if possible.
Because amiodarone stays in the body for a long time, drug interactions are possible for weeks after discontinuation of amiodarone.
Cholestyramine (Questran) can enhance the elimination of amiodarone, probably by binding to it in the gastrointestinal tract.
PREGNANCY: In general, amiodarone should not be administered during pregnancy because there have been reports of hypo- or hyperthyroidism in infants from oral amiodarone use during pregnancy. If amiodarone use is considered essential, however, the patient should be warned of the risk to the fetus.
NURSING MOTHERS: The safe use of amiodarone in women who are breast-feeding during amiodarone therapy has not been established.
SIDE EFFECTS: About 7 out of every 10 patients taking amiodarone will experience some type of side reaction, and between 1 in 20 and 1 in 5 will experience side effects that are severe enough to stop the medication.
The most severe side effects of amiodarone therapy are related to the lungs. These reactions can be fatal. (One in 10 of those that develop lung toxicity will die.) Patients should report any symptoms of cough, fever, or painful breathing. Patients with underlying lung disease do not appear to be at increased risk for the development of amiodarone- associated lung toxicity although their prognosis is worse if they do experience these side effects.
Although quite rare, fatal liver toxicity has occurred with amiodarone therapy. Liver toxicity may manifest as weight loss, enlarged liver (which physicians can diagnose by feeling the liver in the abdomen), ascites (an accumulation of fluid in the abdomen surrounding the abdominal organs), abdominal pain, loss of appetite, or inflammation of the liver (drug hepatitis). In some cases, amiodarone dosage may be reduced. In other cases, amiodarone therapy may need to be stopped.
Amiodarone may cause some heart arrhythmias, although the incidence of amiodarone-induced heart arrhythmias appears to be lower than that due to other medications used to treat arrhythmias. (This might seem ironic since amiodarone is used to treat arrhythmias.) In fewer than 1 of 20 patients with congestive heart failure who receive amiodarone, the failure has been worsened. Low blood pressure may occur.
About 1 or 2 of every 5 patients that receive amiodarone experience some form of nerve toxicity. Symptoms may include imbalance or changes in gait, tremor, uncontrolled movements of the body, numbness in the fingers or toes, dizziness, muscle weakness, tiredness, or loss of coordination. Fortunately, these symptoms are generally not severe enough to justify discontinuance of the drug. Instead, they may disappear with a reduction in dosage.
Up to 1 in 4 patients who receive amiodarone may experience some form of abnormal thyroid function, since the drug molecule is chemically related to thyroid hormone itself. Hypothyroidism (low thyroid) seems to be more common than hyperthyroidism (high thyroid). Symptoms of hyperthyroidism may include sweating, weight loss, trouble sleeping, increased sensitivity to heat, increased heart rate, goiter, tremor or nervousness. Symptoms of hypothyroidism may include intolerance to cold weather, dry skin, weight gain, and unusual tiredness.
About 1 in 10 persons taking amiodarone experiences an exaggerated response to the harmful effects of sunlight, especially to long- wave ultraviolet-A (UVA) light. This effect may even occur through glass windows and/or cotton clothing. Standard sunscreens do not prevent this effect unless they also absorb UVA light. Opaque screens such as zinc oxide or titanium dioxide provide adequate protection. Avoidance of extensive sun exposure and the use of protective clothing should be used to help prevent this adverse reaction.
Long-term administration of amiodarone may occasionally result in a blue-gray discoloration of the skin. This effect seems to be more common in patients with fair skin. This discoloration may reverse slowly when amiodarone is stopped; however, the reversal is sometimes incomplete.
About 1 of every 4 patients that starts amiodarone therapy experiences nausea, vomiting, loss of appetite, constipation, or abdominal pain. These side effects are particularly common during the early "loading phase" when doses are higher. Fortunately, they usually do not warrant stopping the drug. Taking amiodarone with food may reduce the risk of these effects.
Perhaps 1 in 10 patients taking amiodarone experience visual impairment or disturbances, such as halo vision, blurred vision, photophobia, and dry eyes. Corneal deposits (microdeposits) occur in virtually all patients who receive amiodarone for at least 6 months. These are not associated with any symptoms, and there is no relationship of these deposits with any of the visual disturbances described above. Other effects on the eyes are rare and include lens opacities, and abnormalities of the optic nerve.
Amiodarone also has been reported to cause a decrease in libido.
| |
