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Adverse reactions have been very common in virtually all series of patients treated with Cordarone for ventricular arrhythmias with relatively large doses of drug (400 mg/day and above), occurring in about three-fourths of all patients and causing discontinuation in 7 to 18%. The most serious reactions are pulmonary toxicity, exacerbation of arrhythmia, and rare serious liver injury (see “WARNINGS”), but other adverse effects constitute important problems. They are often reversible with dose reduction or cessation of Cordarone treatment. Most of the adverse effects appear to become more frequent with continued treatment beyond six months, although rates appear to remain relatively constant beyond one year. The time and dose relationships of adverse effects are under continued study. Neurologic problems are extremely common, occurring in 20 to 40% of patients and including malaise and fatigue, tremor and involuntary movements, poor coordination and gait, and peripheral neuropathy; they are rarely a reason to stop therapy and may respond to dose reductions or discontinuation (see “PRECAUTIONS”). There have been spontaneous reports of demyelinating polyneuropathy.
Gastrointestinal complaints, most commonly nausea, vomiting, constipation, and anorexia, occur in about 25% of patients but rarely require discontinuation of drug. These commonly occur during high-dose administration (i.e., loading dose) and usually respond to dose reduction or divided doses.
Ophthalmic abnormalities including optic neuropathy and/or optic neuritis, in some cases progressing to permanent blindness, papilledema, corneal degeneration, photosensitivity, eye discomfort, scotoma, lens opacities, and macular degeneration have been reported. (See “WARNINGS”.)
Asymptomatic corneal microdeposits are present in virtually all adult patients who have been on drug for more than 6 months. Some patients develop eye symptoms of halos, photophobia, and dry eyes. Vision is rarely affected and drug discontinuation is rarely needed.
Dermatological adverse reactions occur in about 15% of patients, with photosensitivity being most common (about 10%). Sunscreen and protection from sun exposure may be helpful, and drug discontinuation is not usually necessary. Prolonged exposure to Cordarone occasionally results in a blue-gray pigmentation. This is slowly and occasionally incompletely reversible on discontinuation of drug but is of cosmetic importance only.
Cardiovascular adverse reactions, other than exacerbation of the arrhythmias, include the uncommon occurrence of congestive heart failure (3%) and bradycardia. Bradycardia usually responds to dosage reduction but may require a pacemaker for control. CHF rarely requires drug discontinuation. Cardiac conduction abnormalities occur infrequently and are reversible on discontinuation of drug. The following side-effect rates are based on a retrospective study of 241 patients treated for 2 to 1,515 days (mean 441.3 days).
The Following Side Effects Were Each Reported In 10 To 33% Of Patients
Gastrointestinal: Nausea and vomiting.
The Following Side Effects Were Each Reported In 4 To 9% Of Patients
Dermatologic: Solar dermatitis/photosensitivity.
Neurologic: Malaise and fatigue, tremor/abnormal involuntary movements, lack of coordination, abnormal gait/ataxia, dizziness, paresthesias.
Gastrointestinal: Constipation, anorexia.
Ophthalmologic: Visual disturbances.
Hepatic: Abnormal liver-function tests.
Respiratory: Pulmonary inflammation or fibrosis.
The Following Side Effects Were Each Reported In 1 To 3% Of Patients
Thyroid: Hypothyroidism, hyperthyroidism.
Neurologic: Decreased libido, insomnia, headache, sleep disturbances.
Gastrointestinal: Abdominal pain.
Hepatic: Nonspecific hepatic disorders.
The Following Side Effects Were Each Reported In Less Than 1% Of Patients
In surveys of almost 5,000 patients treated in open U.S. studies and in published reports of treatment with Cordarone, the adverse reactions most frequently requiring discontinuation of Cordarone included pulmonary infiltrates or fibrosis, paroxysmal ventricular tachycardia, congestive heart failure, and elevation of liver enzymes. Other symptoms causing discontinuations less often included visual disturbances, solar dermatitis, blue skin discoloration, hyperthyroidism, and hypothyroidism.
In postmarketing surveillance, serious symptomatic bradycardia has been reported in patients taking amiodarone who initiate treatment with ledipasvir/sofosbuvir or with sofosbuvir with simeprevir, hypotension (sometimes fatal), sinus arrest, anaphylactic/anaphylactoid reaction (including shock), angioedema, urticaria, eosinophilic pneumonia, hepatitis, cholestatic hepatitis, cirrhosis, pancreatitis, acute pancreatitis, renal impairment, renal insufficiency, acute renal failure, acute respiratory distress syndrome in the post-operative setting, bronchospasm, possibly fatal respiratory disorders (including distress, failure, arrest, and ARDS), bronchiolitis obliterans organizing pneumonia (possibly fatal), fever, dyspnea, cough, hemoptysis, wheezing, hypoxia, pulmonary infiltrates and/or mass, pulmonary alveolar hemorrhage, pleural effusion, pleuritis, pseudotumor cerebri, parkinsonian symptoms such as akinesia and bradykinesia (sometimes reversible with discontinuation of therapy), syndrome of inappropriate antidiuretic hormone secretion (SIADH), thyroid nodules/thyroid cancer, toxic epidermal necrolysis (sometimes fatal), erythema multiforme, Stevens-Johnson syndrome, exfoliative dermatitis, bullous dermatitis, drug rash with eosinophilia and systemic symptoms (DRESS), eczema, skin cancer, vasculitis, pruritus, hemolytic anemia, aplastic anemia, pancytopenia, neutropenia, thrombocytopenia, agranulocytosis, granuloma, myopathy, muscle weakness, rhabdomyolysis, demyelinating polyneuropathy, hallucination, confusional state, disorientation, delirium, epididymitis, impotence and dry mouth, also have been reported with amiodarone therapy.
Read the Cordarone (amiodarone hcl tablets) Side Effects Center for a complete guide to possible side effects
In view of the long and variable half-life of amiodarone, potential for drug interactions exists, not only with concomitant medication, but also with drugs administered after discontinuation of amiodarone.
Drugs Inducing TdP or Prolonging QT
Co-administration of amiodarone with drugs known to prolong the QT interval (such as class I and III antiarrhythmics, lithium, certain phenothiazines, tricyclic antidepressants, certain fluoroquinolone and macrolide antibiotics, IV pentamidine, and azole antifungals) increases the risk of Torsades de Points. Avoid concomitant use of drugs that prolong the QT interval.
Drugs Lowering Heart Rate Or Causing Automaticity Or Conduction Disorders
Concomitant use of drugs with depressant effects on the sinus and AV node (e.g., digoxin, beta blockers, verapamil, diltiazem, clonidine) can potentiate the electrophysiologic and hemodynamic effects of amiodarone, resulting in bradycardia, sinus arrest, and AV block. Monitor heart rate in patients on amiodarone and concomitant drugs that slow heart rate.
Effects Of Other Medicinal Products On Amiodarone
Since amiodarone is a substrate for CYP3A and CYP2C8, drugs/substances that inhibit CYP3A (e.g., certain protease inhibitors, loratadine, cimetidine, trazodone) may decrease the metabolism and increase serum concentrations of amiodarone. Concomitant use of CYP3A inducers (rifampin, St. John's Wort), may lead to decreased serum concentrations and loss of efficacy. Consider serial measurement of amiodarone serum concentration during concomitant use of drugs affecting CYP3A activity.
Grapefruit juice given to healthy volunteers increased amiodarone AUC by 50% and C by 84%, and decreased DEA to unquantifiable concentrations. Grapefruit juice inhibits CYP3A-mediated metabolism of oral amiodarone in the intestinal mucosa, resulting in increased plasma levels of amiodarone; therefore, grapefruit juice should not be taken during treatment with oral amiodarone. This information should be considered when transitioning from intravenous to oral amiodarone. Cholestyramine reduces enterohepatic circulation of amiodarone thereby increasing its elimination. This results in reduced amiodarone serum levels and half-life.
Effects Of Amiodarone On Other Medicinal Products
Amiodarone inhibits P-glycoprotein and certain CYP450 enzymes, including CYP1A2, CYP2C9, CYP2D6, and CYP3A. This inhibition can result in unexpectedly high plasma levels of other drugs which are metabolized by those CYP450 enzymes or are substrates of P-glycoprotein. Reported examples of this interaction include the following:
Cyclosporine (CYP3A substrate) administered in combination with oral amiodarone has been reported to produce persistently elevated plasma concentrations of cyclosporine resulting in elevated creatinine, despite reduction in dose of cyclosporine. Monitor cyclosporine drug levels and renal function in patients taking both drugs.
HMG-Co A Reductase Inhibitors
The use of HMG-CoA reductase inhibitors that are CYP3A substrates in combination with amiodarone has been associated with reports of myopathy/rhabdomyolysis. Limit the dose of simvastatin in patients on amiodarone to 20 mg daily. Limit the daily dose of lovastatin to 40 mg. Lower starting and maintenance doses of other CYP3A substrates (e.g., atorvastatin) may be required as amiodarone may increase the plasma concentration of these drugs.
In patients receiving digoxin therapy, administration of oral amiodarone results in an increase in the serum digoxin concentration. Amiodarone taken concomitantly with digoxin increases the serum digoxin concentration by 70% after one day. On initiation of oral amiodarone, the need for digitalis therapy should be reviewed and the dose reduced by approximately 50% or discontinued. If digitalis treatment is continued, serum levels should be closely monitored and patients observed for clinical evidence of toxicity.
The metabolism of quinidine, procainamide, flecainide can be inhibited by amiodarone. Amiodarone taken concomitantly with quinidine increases quinidine serum concentration by 33% after two days. Amiodarone taken concomitantly with procainamide for less than seven days increases plasma concentrations of procainamide and n-acetyl procainamide by 55% and 33%, respectively. In general, any added antiarrhythmic drug should be initiated at a lower than usual dose with careful monitoring.
Combination of amiodarone with other antiarrhythmic therapy should be reserved for patients with lifethreatening ventricular arrhythmias who are incompletely responsive to a single agent or incompletely responsive to amiodarone. During transition to amiodarone the dose levels of previously administered agents should be reduced by 30 to 50% several days after the addition of amiodarone, when arrhythmia suppression should be beginning. The continued need for the other antiarrhythmic agent should be reviewed after the effects of amiodarone have been established, and discontinuation ordinarily should be attempted. If the treatment is continued, these patients should be particularly carefully monitored for adverse effects, especially conduction disturbances and exacerbation of tachyarrhythmias, as amiodarone is continued. In amiodarone-treated patients who require additional antiarrhythmic therapy, the initial dose of such agents should be approximately half of the usual recommended dose.
Metabolism of lidocaine (CYP3A substrate) can be inhibited by amiodarone resulting in increased lidocaine concentrations. Sinus bradycardia and seizure has been reported in patients receiving concomitant lidocaine and amiodarone.
Potentiation of warfarin-type (CYP2C9 and CYP3A substrate) anticoagulant response is almost always seen in patients receiving amiodarone and can result in serious or fatal bleeding. Since the concomitant administration of warfarin with amiodarone increases the prothrombin time by 100% after 3 to 4 days, the dose of the anticoagulant should be reduced by one-third to one-half, and prothrombin times should be monitored closely.
A potential interaction between clopidogrel and amiodarone resulting in ineffective inhibition of platelet aggregation has been reported.
Dabigatran etexilate when taken concomitantly with amiodarone may result in elevated serum concentration of dabigatran.
Fentanyl (CYP3A substrate) in combination with amiodarone may cause hypotension, bradycardia, and decreased cardiac output.
Increased steady-state levels of phenytoin during concomitant therapy with amiodarone have been reported. Monitor phenytoin levels in patients taking both drugs.
Dextromethorphan is a substrate for both CYP2D6 and CYP3A. Amiodarone inhibits CYP2D6 and CYP3A. Chronic ( > 2 weeks) amiodarone treatment impairs metabolism of dextromethorphan leading to increased serum concentration.
Read the Cordarone Drug Interactions Center for a complete guide to possible interactions
Last reviewed on RxList: 9/14/2016
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