Amiodarone is an antiarrhythmic agent which inhibits stimulation, prolongs action potential and refractory period in myocardial tissues. It also decreases AV conduction and sinus node function. Sinus rate is reduced by 15-20%, PR and QT intervals are increased. Amiodarone can cause marked sinus bradycardia or sinus arrest and heart block. Amiodarone may exert a mild negative inotropic effect at high doses if given intravenously.
If you are about to start a drug therapy, the risk and benefit ratio of taking the drug should be considered. This is a decision that your doctor will make with your active participation.
Amiodarone should be used cautiously as it exerts multiple actions:
Prolongs APD and Q-T interval attributable to block of myocardial delayed rectifier K+ channels. This also appears to reduce non-uniformity of refractoriness among different fibers.
Preferentially blocks inactivated Na+ channels with the relatively rapid rate of channel recovery. More effective in depressing conduction in cells that are partially depolarized or have longer APD.
Inhibits myocardial Ca2+ channels and has noncompetitive beta-adrenergic blocking property.
There are some important factors such as drug interaction, metabolic impairment, hypersensitivity reaction, pregnancy, lactation etc. which may alter the drug action.
Certain drugs should not be used concurrently with such medications. It is always recommended to consult with your doctor if you are in need of some drugs for another health problem.
You should know about following drug interactions to get rid of further complications:
Amiodarone can increase digoxin and warfarin levels by reducing their renal clearance.
The additive effect can occur in patients receiving beta blockers or calcium channel blockers (e.g. verapamil and diltiazem).
Possible increased risk of adverse effects when used with anesthetic agents.
Monitoring of plasma levels of amiodarone is recommended when used with HIV protease inhibitors.
Cimetidine may increase serum levels of amiodarone.
Concurrent use may increase serum levels of ciclosporin.
May increase risk of myopathy or rhabdomyolysis when used with HMG-CoA reductase inhibitors.
Rifampicin may reduce the serum levels of amiodarone.
Sometimes the presence of other health disorders affects the beneficial effects of this medicine and even may cause serious complications. Make sure you mention your doctor if you have any other medical problems.
The use of amiodarone is contraindicated in hypersensitivity to amiodarone or iodine, severe sinus node dysfunction, 2nd and 3rd-degree heart block (except in patients with a functioning artificial pacemaker), cardiogenic shock, and pregnancy.
There is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.
3 Proper Usage
Medicines should be used following the directions were given by a doctor. The dose of this medicine will vary according to patient’s condition or requirements.
You should follow the doctor's directions and advice. The amount of medicine that you take should not exceed the maximum therapeutic dose.
Also, the frequency of your daily drug administration and the duration of drug therapy depend on the particular medical problem for which you are taking the medicine.
Amiodarone is commonly used as an antiarrhythmic for its high and broad spectrum efficacy, despite its organ toxicity in the long-term use.
This drug is suitable for long-term prophylactic therapy because of its long duration of action that has been found to reduce sudden cardiac death.
Amiodarone has been found effective in a wide range of ventricular and supraventricular arrhythmias.
In order to treat ventricular arrhythmias, the therapeutic dose in an adult is 800-1600 mg/day in 1-2 divided doses for 1-3 weeks until an initial therapeutic response is achieved, then reduce dose to 600-800 mg/day in 1-2 divided doses for 1 month.
Here, the maintenance dose is 400 mg/day. Lower doses may be used for supraventricular arrhythmias. Close monitoring of the patient is recommended. Dosage reduction may be necessary for hepatic impairment.
Always try to take your medicine in time. If you miss any dose of this medicine, you should take it as soon as possible. But if it is time for your next dose, then you should skip the missed dose and go back to your regular treatment schedule.
You should store the medicine in a closed container at room temperature away from heat, moisture, and direct light. All kinds of medicines should be kept out of the reach of children.
Outdated medicine must be disposed of by an appropriate way.
4 Precautions to Take
Regular visits are recommended to make sure this medicine is working properly or not while you are undergoing amiodarone therapy.
Some important measures should be taken if you feel any discomfort following this drug therapy. If you have an electrolyte imbalance, you should correct it before starting treatment.
In addition, avoid excessive sunlight exposure due to increased risk of photosensitivity.
Close monitoring is recommended as amiodarone may worsen arrhythmia especially when used concurrently with other anti-arrhythmic drugs or drugs that prolong QT interval.
Corneal refractive laser surgery is not recommended in patients on amiodarone treatment. Monitoring for pulmonary toxicity and liver function tests should be carried out regularly.
There are some unwanted side-effects associated with each drug that usually do not need medical attention.
These side-effects usually go away during the treatment episode as your body adjusts to the medicine. Additionally, your health care professional may advise you about the ways how to prevent or reduce those unwanted side-effects.
Sometimes you may need to consult with the doctor if you feel any serious toxic effect:
Fall in BP, bradycardia, and myocardial depression occurs on drug cumulation.
Nausea, a gastrointestinal upset may attend oral medication, especially during the loading phase.
Corneal microdeposits are common with long-term use but are reversible on discontinuation.
Pulmonary alveolitis and fibrosis is the most serious toxicity of prolonged use but is rare if daily dose is kept below 200 mg.
Amiodarone interferes with thyroid function in many ways including inhibition of peripheral conversion of T4 to T3: goiter, hypothyroidism, and rarely hyperthyroidism may develop with chronic use.
Photosensitization and skin pigmentation occurs in about 10% patients.
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