Antiarrhythmics · Cardiovascular
Amiodarone
Cordarone® · Nexterone®(brand names vary by market)
The most effective antiarrhythmic there is, and the most toxic organ by organ.
Also: injection, infusion
Mechanism
Blocks potassium, sodium and calcium channels and antagonises beta receptors: every antiarrhythmic class in one molecule, which is why it works when others fail.
Indications
- Ventricular arrhythmia
- Atrial fibrillation, rhythm control
- Cardiac arrest with shock-refractory ventricular fibrillation
Formulations
Dosing concepts
Loading
Its enormous volume of distribution means loading takes weeks orally; steady state is not a same-week event, which is also why toxicity appears long after starting.
Stopping
Because of that same reservoir, effects and interactions persist for months after the last dose. Stopping it does not stop it.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~50%, erratic
- Half-life
- Weeks to months (commonly quoted as around 40 to 60 days)
- Elimination
- hepatic: CYP3A4; itself an inhibitor of CYP2C9, CYP2D6 and P-glycoprotein, which is why it raises warfarin and digoxin
- Protein binding
- >95%
Highly lipophilic, concentrating in fat, liver, lung and thyroid: the distribution predicts the toxicity list.
Play with these concepts in the PK LabAdverse effects
- Thyroid dysfunction, both directionscommon & seriousEach molecule carries two iodine atoms; both hypo- and hyperthyroidism occur, and the hyperthyroid form can be difficult to treat.
- Pulmonary toxicityseriousInsidious cough and breathlessness; the most feared effect and reversible only if caught early.
- Hepatotoxicityserious
- Corneal microdepositscommonAlmost universal, usually asymptomatic, rarely a reason to stop.
- Blue-grey skin discolouration and photosensitivitycommon
- Bradycardia and QT prolongationcommon & serious
- Peripheral neuropathyserious
Contraindications & precautions
Contraindications
- Severe sinus node disease or high-grade AV block without a pacemaker
- Iodine hypersensitivity
- Thyrotoxicosis
Precautions
- Pre-existing lung disease
- Hepatic impairment
- Concurrent warfarin, digoxin or statins
- Any other QT-prolonging drug
Interactions
Monitoring
Thyroid function
Both directions occur and neither is obvious clinically · Baseline then every 6 months
Liver enzymes
Hepatotoxicity · Baseline then every 6 months
Chest imaging and respiratory symptoms
Pulmonary toxicity · Baseline, then whenever there is a new cough or breathlessness
ECG including QT
Proarrhythmia
INR if on warfarin
It roughly doubles the effect over weeks
Counselling points
- You will need regular blood tests for as long as you take this, and they matter.
- Report any new cough or breathlessness promptly.
- Use sun protection; skin reactions and discolouration are common.
- Tell any clinician you take this, even months after stopping, because it stays in the body a very long time.
Clinical pearls
- A new cough in a patient on amiodarone is pulmonary toxicity until proven otherwise, and the diagnosis is missed constantly because it looks like heart failure or infection.
- Starting amiodarone in a warfarin patient means anticipating the INR rise rather than reacting to it; the interaction develops over weeks as the reservoir fills.
- The half-life is measured in weeks, so a loading regimen is not impatience, it is pharmacokinetics.
References & review
- Amiodarone product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.