Amiodarone
An iodine-rich antiarrhythmic, mainly class III, kept for serious ventricular and atrial arrhythmias because of its many organ toxicities.
Drug card
- How it works
- Blocking cardiac potassium channels, so repolarization and the QT lengthen
- Used for
- Recurrent ventricular fibrillation or unstable VT
- Atrial fibrillation or flutter when other drugs fail
- Known for
- Lung toxicity: pneumonitis and fibrosis
- Underactive or overactive thyroid
- Corneal microdeposits, with halos or blurring
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does amiodarone work?
Mainly lengthens the action potential and refractory period by blocking potassium channels, but it also blocks sodium and calcium channels and has a non-competitive anti-adrenergic action, so it shows features of all four Vaughan Williams classes. Its half-life runs from weeks to months, so effects and interactions persist long after it is stopped.
Uses
What is amiodarone used for?
- Recurrent ventricular fibrillation or unstable VT
- Atrial fibrillation or flutter when other drugs fail
Side effects
Side effects of amiodarone
- Lung toxicity: pneumonitis and fibrosisKnown forSerious
- Underactive or overactive thyroidKnown forSerious
- Corneal microdeposits, with halos or blurringKnown for
- Liver injury, sometimes fatalSerious
- Optic neuropathy, which can cause blindnessSerious
- Sensitivity to sunlight
- Blue-gray discoloration of sun-exposed skin
- Slow heart rate or sinus arrestSerious
- Worsened arrhythmia, including torsades de pointesSerious
- QT prolongationSerious
- Peripheral neuropathy
- Nausea, vomiting and constipation
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Lungs, liver, thyroid and eyes are checked before starting and regularly during treatment.
- It raises digoxin levels and the effect of warfarin; sofosbuvir-based regimens can cause severe bradycardia with it.
- Contraindicated in cardiogenic shock, sick sinus syndrome or AV block without a pacemaker, and iodine allergy.
- Pregnancy: it can harm the fetus, including the fetal thyroid.
Good to know: Its toxicity restricts it to arrhythmias that are life-threatening or resist other drugs, and each tablet carries a large load of iodine.
Remember it
A way to remember it
On amiodarone, check PFTs, LFTs and TFTs.
Its big organ toxicities are in the lungs (pneumonitis and fibrosis), the liver and the thyroid, so pulmonary, liver and thyroid function tests are done before and during treatment; the eyes and skin are watched too.
A mnemonic widely used in teaching
Its class
Class III antiarrhythmics
They block the cardiac potassium channels that repolarize heart muscle, so the action potential and the refractory period lengthen and the QT interval prolongs. Longer refractoriness suppresses ventricular and atrial tachyarrhythmias, but the long QT can itself set off torsades de pointes. Sotalol also blocks beta receptors, and amiodarone acts on all four Vaughan Williams classes.
Easily mixed up with beta blockers, non-dihydropyridine calcium channel blockers and cardiac glycosides.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Amiodarone hydrochloride tablets: label (DailyMed)
- Amiodarone hydrochloride injection: label (DailyMed)
- Amiodarone hydrochloride 200 mg tablets: SmPC (emc)
- Amiodarone (NCI Thesaurus)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Heart failure, rhythm and angina
Amiodarone is one of 10 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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