|Trade names||Cordarone, Nexterone, others|
|By mouth or intravenous|
|ATC code||C01BD01 (WHO)|
|Biological half-life||58 d (range 15-142 d)|
|Excretion||Primarily liver and bile|
|Chemical and physical data|
|Molar mass||645.31 g/mol|
|3D model (Jmol)||Interactive image|
Amiodarone is an antiarrhythmic medication used to treat and prevent a number of types of irregular heartbeats. This includes ventricular tachycardia (VT), ventricular fibrillation (VF), and wide complex tachycardia, as well as atrial fibrillation and paroxysmal supraventricular tachycardia. It can be given by mouth, intravenously, or intraosseously. When used by mouth it can take a few weeks for effects to begin.
Common side effects include feeling tired, tremor, nausea, and constipation. As amiodarone can have serious side effects, it is mainly recommended only for significant ventricular arrhythmias. Serious side effects include lung toxicity such as interstitial pneumonitis, liver problems, heart arrhythmias, vision problems, thyroid problems, and death. If taken during pregnancy or breastfeeding it can cause problems in the baby. It is a class III antiarrhythmic medication. It works partly by increasing the time before a heart cell can contract again.
Amiodarone was first made in 1961 and came into medical use in 1962 for chest pain believed to be related to the heart. It was pulled from the market in 1967 due to side effects. In 1974 it was found to be useful for arrhythmias and reintroduced. It is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system. It is available as a generic medication. In the developing world the wholesale cost as of 2014 is about 0.06 to 0.26 USD per day. In the United States a typical month supply is between 100 and 200 USD.
Amiodarone has been used both in the treatment of acute life-threatening arrhythmias as well as the chronic suppression of arrhythmias. It is used both in supraventricular arrhythmias and ventricular arrhythmias.
Defibrillation is the treatment of choice for ventricular fibrillation (VF) and ventricular tachycardia resulting in cardiac arrest. However, amiodarone has been used in shock-refractory VF. The 2010 guidelines of the American Heart Association included amiodarone as a second line agent (after epinephrine or vasopressin). They believed that amiodarone was more effective than lidocaine in VF or pulseless ventricular tachycardia.
Amiodarone may be used in the treatment of ventricular tachycardia in certain instances. Individuals with hemodynamically unstable ventricular tachycardia should not initially receive amiodarone. These individuals should be cardioverted.
Amiodarone can be used in individuals with hemodynamically stable ventricular tachycardia. In these cases, amiodarone can be used regardless of the individual's underlying heart function and the type of ventricular tachycardia; it can be used in individuals with monomorphic ventricular tachycardia, but is contraindicated in individuals with polymorphic ventricular tachycardia as it is associated with a prolonged QT interval which will be made worse with anti-arrhythmic drugs.
Individuals who have undergone open heart surgery are at an increased risk of developing atrial fibrillation (or AF) in the first few days post-procedure. In the ARCH trial, intravenous amiodarone (2 g administered over 2 d) has been shown to reduce the incidence of atrial fibrillation after open heart surgery when compared to placebo. However, clinical studies have failed to demonstrate long-term efficacy and have shown potentially fatal side effects such as pulmonary toxicities. While amiodarone is not approved for AF by the FDA, it is a commonly prescribed off-label treatment due to the lack of equally effective treatment alternatives.
So called 'acute onset atrial fibrillation', defined by the North American Society of Pacing and Electrophysiology (NASPE) in 2003, responds well to short duration treatment with amiodarone. This has been demonstrated in seventeen randomised controlled trials, of which five included a placebo arm. The incidence of severe side effects in this group is low.
The benefit of amiodarone in the treatment of atrial fibrillation in the critical care population has yet to be determined but it may prove to be the agent of choice where the patient is hemodynamically unstable and unsuitable for DC cardioversion. It is recommended in such a role by the UK government's National Institute for Health and Clinical Excellence (NICE).
Women who are pregnant or may become pregnant are strongly advised to not take amiodarone. Since amiodarone can be expressed in breast milk, women taking amiodarone are advised to stop nursing.
Individuals with baseline depressed lung function should be monitored closely if amiodarone therapy is to be initiated.
Amiodarone can worsen the cardiac arrhythmia brought on by digitalis toxicity.
Amiodarone has numerous side effects. Most individuals administered amiodarone on a chronic basis will experience at least one side effect.
Side effects of amiodarone include various pulmonary effects. The most serious reaction that is due to amiodarone is interstitial lung disease. Risk factors include high cumulative dose, more than 400 milligrams per day, duration over two months, increased age, and preexisting pulmonary disease. Some individuals were noted to develop pulmonary fibrosis after a week of treatment, while others did not develop it after years of continuous use. Common practice is to avoid the agent if possible in individuals with decreased lung function.
Induced abnormalities in thyroid function are common. Both under- and overactivity of the thyroid may occur.
Amiodarone is structurally similar to thyroxine and also contains iodine. Both of these contribute to the effects of amiodarone on thyroid function. Amiodarone also causes an anti-thyroid action, via Wolff–Chaikoff effect, due its large amount of iodine in its molecule, which causes a particular "cardiac hypothyroidism " with bradycardia and arrhythmia.
- Hypothyroidism (slowing of the thyroid) occurs frequently; in the SAFE trial, which compared amiodarone with other medications for the treatment of atrial fibrillation, biochemical hypothyroidism (as defined by a TSH level of 4.5-10 mU/l) occurred in 25.8% of the amiodarone-treated group as opposed to 6.6% of the control group (taking placebo or sotalol). Overt hypothyroidism (defined as TSH >10 mU/l) occurred at 5.0% compared to 0.3%; most of these (>90%) were detected within the first six months of amiodarone treatment.
- Hyperthyroidism (an overactive thyroid, due to the Jod-Basedow Effect) can also occur. However, in the SAFE trial, the increased rate of hyperthyroidism (5.3% compared to 2.4%) was not statistically significant. Most hyperthyroid patients (defined as TSH <0.35 mU/l) were asymptomatic.
Thyroid uptake measurements (I-123 or I-131), which are used to differentiate causes of hyperthyroidism, are generally unreliable in patients who have been taking amiodarone. Because of the high iodine content of amiodarone, the thyroid gland is effectively saturated, thus preventing further uptake of isotopes of iodine. However, the radioactive iodine uptake (nuclear thyroid uptake test) may still be helpful in the diagnosis and management of amiodarone-induced hyperthyroidism.
Corneal micro-deposits (cornea verticillata, also called vortex or whorl keratopathy) are almost universally present (over 90%) in individuals taking amiodarone longer than 6 months, especially doses greater than 400 mg/day. These deposits typically do not cause any symptoms. About 1 in 10 individuals may complain of a bluish halo. Anterior subcapsular lens deposits are relatively common (50%) in higher doses (greater than 600 mg/day) after 6 months of treatment. Optic neuropathy, nonarteritic anterior ischemic optic neuropathy (N-AION), occurs in 1-2% of people and is not dosage dependent. Bilateral optic disc swelling and mild and reversible visual field defects can also occur. Loss of eyelashes has been linked to amiodarone use.
Long-term administration of amiodarone (usually more than eighteen months) is associated with a light-sensitive blue-grey discoloration of the skin; such patients should avoid exposure to the sun and use sunscreen that protects against ultraviolet-A and -B. The discoloration will slowly improve upon cessation of the drug, however, the skin colour may not return completely
Amiodarone is sometimes responsible for epididymitis, a condition of the epididymis, and is normally associated with bacterial infections but which can also occur as a non-bacterial inflammatory condition. Amiodarone accumulates in the head of the organ and can cause unilateral or bilateral inflammation. It tends to resolve if amiodarone is stopped.
Some cases of gynecomastia have been reported with men on amiodarone.
A study published in 2013 showed a possible association between amiodarone and an increased risk of cancer, especially in males, with a dose-dependent effect.
Amiodarone is extensively metabolized in the liver by cytochrome P450 3A4, and can affect the metabolism of numerous other drugs. It interacts with digoxin, warfarin, phenytoin, and others. The major metabolite of amiodarone is desethylamiodarone (DEA), which also has antiarrhythmic properties. The metabolism of amiodarone is inhibited by grapefruit juice, leading to elevated serum levels of amiodarone.
On August 8, 2008, the FDA issued a warning of the risk of rhabdomyolysis, which can lead to kidney failure or death, when simvastatin is used with amiodarone. This interaction is dose-dependent with simvastatin doses exceeding 20 mg. This drug combination especially with higher doses of simvastatin should be avoided.
The pharmacokinetics of numerous drugs, including many that are commonly administered to individuals with heart disease, are affected by amiodarone. Particularly, doses of digoxin should be halved in individuals taking amiodarone.
Amiodarone potentiates the action of warfarin by inhibiting the clearance of both (S) and (R) warfarin. Individuals taking both of these medications should have their warfarin doses adjusted based off their dosing of amiodarone, and have their anticoagulation status (measured as prothrombin time (PT) and international normalized ratio (INR)) measured more frequently. Dose reduction of warfarin is as follows: 40% reduction if amiodarone dose is 400 mg daily, 35% reduction if amiodarone dose is 300 mg daily, 30% reduction if amiodarone dose is 200 mg daily, and 25% reduction if amiodarone dose is 100 mg daily. The effect of amiodarone on the warfarin concentrations can be as early as a few days after initiation of treatment; however, the interaction may not peak for up to seven weeks.
In March 2015, Gilead Sciences e-mailed warnings to health care providers about nine patients that began taking its hepatitis C drugs Harvoni (ledipasvir/sofosbuvir) or Sovaldi (sofosbuvir) along with the heart treatments amiodarone, Bristol-Myers Squibb's Daklinza (daclatasvir), or Johnson & Johnson's Olysio (simeprevir) developed abnormally slow heartbeats and one died of cardiac arrest. Three required a pacemaker to be inserted. Gilead said the combinations aren't recommended and product labels will be updated.
Excretion is primarily hepatic and biliary with almost no elimination via the renal route and it is not dialyzable [Package Insert- Pacerone(R)]. Elimination half-life average of 58 days (ranging from 25–100 days [Remington: The Science and Practice of Pharmacy 21st edition]) for amiodarone and 36 days for the active metabolite, desethylamiodarone (DEA) [Package Insert- Pacerone(R)]. There is 10-50% transfer of amiodarone and DEA in the placenta as well as presence in breast milk [Package Insert- Pacerone(R)]. Accumulation of amiodarone and DEA occurs in adipose tissue and highly perfused organs (i.e. liver, lungs) [Package Insert- Pacerone(R)], therefore, if an individual was taking amiodarone on a chronic basis, if it is stopped it will remain in the system for weeks to months.
Mechanism of action
Amiodarone is categorized as a class III antiarrhythmic agent, and prolongs phase 3 of the cardiac action potential, the repolarization phase where there is normally decreased calcium permeability and increased potassium permeability. It has numerous other effects however, including actions that are similar to those of antiarrhythmic classes Ia, II, and IV.
Amiodarone shows beta blocker-like and calcium channel blocker-like actions on the SA and AV nodes, increases the refractory period via sodium- and potassium-channel effects, and slows intra-cardiac conduction of the cardiac action potential, via sodium-channel effects.
Amiodarone chemically resembles thyroxine (thyroid hormone), and its binding to the nuclear thyroid receptor might contribute to some of its pharmacologic and toxic actions.
The original observation that amiodarone's progenitor molecule, khellin, had cardioactive properties, was made by the Russian physiologist Gleb von Anrep while working in Cairo in 1946. Khellin is obtained from a plant extract of Khella or Ammi visnaga, a common plant in north Africa. Anrep noticed that one of his technicians had been cured of anginal symptoms after taking khellin, then used for various, non-cardiac ailments. This led to efforts by European pharmaceutical industries to isolate an active compound. Amiodarone was initially developed in 1961 at the Labaz company, Belgium, by chemists Tondeur and Binon, who were working on preparations derived from khellin. It became popular in Europe as a treatment for angina pectoris.
As a doctoral candidate at Oxford University, Bramah Singh determined that amiodarone and sotalol had antiarrhythmic properties and belonged to a new class of antiarrhythmic agents (what would become the class III antiarrhythmic agents). Today the mechanisms of action of amiodarone and sotalol have been investigated in more detail. Both drugs have been demonstrated to prolong the duration of the action potential, prolonging the refractory period, by interacting among other cellular function with K+ channels.
Based on Singh's work, the Argentinian physician Mauricio Rosenbaum began using amiodarone to treat his patients who suffered from supraventricular and ventricular arrhythmias, with impressive results. Based on papers written by Rosenbaum developing Singh's theories, physicians in the United States began prescribing amiodarone to their patients with potentially life-threatening arrhythmias in the late 1970s. By 1980, amiodarone was commonly prescribed throughout Europe for the treatment of arrhythmias, but in the U.S. amiodarone remained unapproved by the Food and Drug Administration, and 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 American physicians if it was not approved. In December 1985, amiodarone was approved by the FDA for the treatment of arrhythmias. This makes amiodarone one of the few drugs approved by the FDA without rigorous randomized clinical trials.
Amiodarone may be an acronym for its IUPAC name (2-butyl-1-benzofuran-3-yl)-[4-[2-(diethylamino)ethoxy]-3,5-diiodophenyl]methanone, where ar is a placeholder for phenyl. This is partially supported by dronedarone which is noniodinated benzofuran derivative of amiodarone, where the arylmethanone is conserved.
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). It is also available under the trade name Aratac (produced by Alphapharm Pty Ltd) in Australia and New Zealand, and further in Australia under the brands Cardinorm and Rithmik as well as a number of generic brands. Also Arycor in South Africa (Produced by Winthrop Pharmaceuticals.). In South America, it is known as Atlansil and is produced by Roemmers.
In India amiodarone is marketed(produced by Cipla Pharmaceutical) under the brand name Tachyra. It is also available in intravenous ampules and vials.
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.
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