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Class III Antiarrhythmic (Iodine-containing) Pregnancy: UK SPC §4.6: 'There are insufficient data on the use of amiodarone during pregnancy in humans to judge any possible toxicity. However, in view of its effect on the foetal thyroid gland, amiodarone is contraindicated during pregnancy, except in exceptional circumstances. If, because of the long half-life of amiodarone, discontinuation of the drug is considered prior to planned conception, the real risk of re-occurrence of life threatening arrhythmias should be weighed against the possible hazard for the foetus.' Lactation: 'Amiodarone is excreted into the breast milk in significant quantities and therefore breast-feeding is contraindicated.' US §8.1 adds: 'Available data from post-marketing reports and published case series indicate that amiodarone use in pregnant women may increase the risk for fetal adverse effects including neonatal hypo- and hyperthyroidism, neonatal bradycardia, neurodevelopmental abnormalities, preterm birth and fetal growth restriction. Amiodarone and its metabolite, desethylamiodarone (DEA), cross the placenta. Untreated underlying arrhythmias, including ventricular arrhythmias, during pregnancy pose a risk to the mother and fetus.'

Amiodarone Hydrochloride

Brand names: Cordarone X

Amiodarone hydrochloride is the salt form of the class III antiarrhythmic amiodarone, available as oral and intravenous preparations for serious atrial and ventricular tachyarrhythmias.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: ORAL, arrhythmia control (UK SPC): initial stabilisation 200 mg three times a day, which may be continued for 1 week; the dosage should then be reduced to 200 mg twice daily for a further week; maintenance thereafter 200 mg daily, or less if appropriate, titrated to the minimum required to maintain control of the arrhythmia
Route: Oral (200 mg tablets). SCOPE: both fetched labels are ORAL amiodarone only — the UK SPC states 'Method of administration For oral use.' The intravenous VT/VF regimens shown on the existing page are NOT covered by anything in this bundle and are not reproduced here.
Frequency: Three times daily during week 1, twice daily during week 2, then once daily for maintenance
Verbatim source wording (UK SPC §4.2, Adults): 'It is particularly important that the minimum effective dose be used. In all cases the patient's management must be judged on the individual response and wellbeing... Initial Stabilisation Treatment should be started with 200mg, three times a day and may be continued for 1 week. The dosage should then be reduced to 200mg, twice daily for a further week. Maintenance After the initial period the dosage should be reduced to 200mg daily, or less if appropriate. Rarely, the patient may require a higher maintenance dose. The dosage should be titrated to the minimum required to maintain control of the arrhythmia. The maintenance dose should be regularly reviewed, especially where this exceeds 200 mg daily.' NO MAXIMUM: neither label states an absolute ceiling with an explicit maximum cue for the oral regimen, so maxDose is deliberately left empty — the UK SPC instead says 'Rarely, the patient may require a higher maintenance dose', which is not a ceiling. US LABEL DIFFERS SUBSTANTIALLY and is recorded here for cross-reference only, NOT merged into the dose above (Pacerone §2): 'Initiate treatment with a loading dose of 800 to 1600 mg/day until initial therapeutic response occurs (usually 1 to 3 weeks). Once adequate arrhythmia control is achieved, or if side effects become prominent, reduce Pacerone tablets dose to 600 to 800 mg/day for one month and then to the maintenance dose, usually 400 mg/day.' US administration note: 'Administer Pacerone tablets consistently with regard to meals... Administration of Pacerone tablets in divided doses with meals is suggested for total daily doses of 1000 mg or higher, or when gastrointestinal intolerance occurs.' PHARMACOKINETIC CONTEXT (UK §4.2): 'Amiodarone is strongly protein bound and has an average plasma half-life of 50 days (reported range 20-100 days). Therefore, sufficient time must be allowed for a new distribution equilibrium to be achieved between adjustments of dosage.' WITHDRAWAL (UK §4.2): 'Side effects slowly disappear as tissue levels fall. Following drug withdrawal, residual tissue bound amiodarone may protect the patient for up to a month. However, the likelihood of recurrence of arrhythmia during this period should be considered.' ELDERLY (UK §4.2): 'As with all patients it is important that the minimum effective dose is used. Whilst there is no evidence that dosage requirements are different for this group of patients they may be more susceptible to bradycardia and conduction defects if too high a dose is employed. Particular attention should be paid to monitoring thyroid function.' BEFORE STARTING (US §2): 'Obtain baseline chest x-ray, pulmonary function tests, thyroid function tests, and liver aminotransferases. Correct hypokalemia, hypomagnesemia, and hypocalcemia before initiating treatment.' The UK §4.4 adds: 'Before starting amiodarone, it is recommended to perform an ECG and serum potassium measurement.'

Dose adjustments

Renal

Not stated — no renal-impairment dosing statement appears in any fetched section of either label (UK §4.2, §4.3, §4.4, §4.6, §4.8; US §2, §3, §4, §5, §6, §7, §8.1, §8.4, §8.5). The UK §4.8 lists 'increase in blood creatinine' (very rare) as an adverse effect, not a dosing rule; the US §8.5 geriatric section notes only that dose selection should be cautious 'reflecting the greater frequency of decreased hepatic, renal, or cardiac function'. Verify against the full SPC before advising.

Hepatic

Not stated as a dose adjustment — neither fetched label gives a hepatic-impairment dosing rule. What is stated is hepatic TOXICITY and its monitoring: UK §4.8 lists, very commonly, 'isolated increase in serum transaminases, which is usually moderate (1.5 to 3 times normal range), occurring at the beginning of therapy. It may return to normal with dose reduction or even spontaneously'; commonly, 'acute liver disorders with high serum transaminases and/or jaundice, including hepatic failure, which are sometimes fatal'; and very rarely 'chronic liver disease (pseudo alcoholic hepatitis, cirrhosis), sometimes fatal'. The US label requires baseline liver aminotransferases before initiation (§2). Verify against the full SPC before advising.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance, iodine, or to any of the excipients listed in section 6.1 — 'one 200mg tablet contains approximately 75mg iodine' (UK SPC §4.3)
  • Sinus bradycardia and sino-atrial heart block (UK SPC §4.3)
  • Severe conduction disturbances (high grade AV block, bifascicular or trifascicular block) or sinus node disease — the tablets 'should be used only in conjunction with a pacemaker' (UK SPC §4.3)
  • Evidence or history of thyroid dysfunction — 'Thyroid function tests should be performed in all patients prior to therapy' (UK SPC §4.3)
  • Combination with drugs which may induce Torsades de Pointes (UK SPC §4.3, cross-referring to §4.5)
  • Lactation (UK SPC §4.3 and §4.6 — 'Amiodarone is excreted into the breast milk in significant quantities and therefore breast-feeding is contraindicated')
  • Pregnancy, 'except in exceptional circumstances' (UK SPC §4.3 and §4.6)
  • Cross-check, US label §4 (Pacerone) adds: cardiogenic shock; and 'Sick sinus syndrome, second- or third-degree atrioventricular block, bradycardia leading to syncope without a functioning pacemaker'

Side effects

  • Eye, very common (UK SPC §4.8): 'corneal microdeposits usually limited to the area under the pupil, which are usually only discernable by slit-lamp examinations. They may be associated with coloured halos in dazzling light or blurred vision... The deposits are considered essentially benign and do not require discontinuation of amiodarone.' Very rare: 'optic neuropathy/neuritis that may progress to blindness'
  • Endocrine, common: hypothyroidism; 'hyperthyroidism, sometimes fatal'. Very rare: syndrome of inappropriate antidiuretic hormone secretion (SIADH)
  • Hepatobiliary, very common: 'isolated increase in serum transaminases, which is usually moderate (1.5 to 3 times normal range), occurring at the beginning of therapy'. Common: 'acute liver disorders with high serum transaminases and/or jaundice, including hepatic failure, which are sometimes fatal'. Very rare: 'chronic liver disease (pseudo alcoholic hepatitis, cirrhosis), sometimes fatal'
  • Cardiac, common: 'bradycardia, generally moderate and dose-related'. Uncommon: 'onset or worsening of arrhythmia, sometimes followed by cardiac arrest'; conduction disturbances (sinoatrial block, AV block of various degrees). Very rare: 'marked bradycardia or sinus arrest in patients with sinus node dysfunction and/or in elderly patients'. Not known: torsade de pointes
  • Gastrointestinal, very common: 'benign gastrointestinal disorders (nausea, vomiting, dysgeusia) usually occurring with loading dosage and resolving with dose reduction'. Common: constipation. Uncommon: dry mouth. Not known: pancreatitis/acute pancreatitis
  • Blood and lymphatic, very rare: haemolytic anaemia, aplastic anaemia, thrombocytopenia. Not known: neutropenia, agranulocytosis. 'In patients taking amiodarone there have been incidental findings of bone marrow granulomas. The clinical significance of this is unknown'
  • Immune, not known: 'angioneurotic oedema (Quincke's Oedema)', 'anaphylactic shock/anaphylactoid reaction including shock'. Investigations, very rare: increase in blood creatinine. Injury, not known: 'Primary graft dysfunction post cardiac transplant'
  • Pulmonary toxicity — the UK §4.4 states amiodarone 'can cause serious adverse reactions affecting the eyes, heart, lung, liver, thyroid gland, skin and peripheral nervous system'; the US §5.2 quantifies it: 'a clinical syndrome of cough and progressive dyspnea... Rates of pulmonary toxicity have been reported to be as high as 17% and is fatal in about 10% of cases'
  • Cross-check, US label: 'The most common reactions (>1%) leading to discontinuation of amiodarone include pulmonary toxicity, paroxysmal ventricular tachycardia, congestive heart failure, and elevation of liver enzymes' (§6); the US Highlights also list peripheral neuropathy, and photosensitivity and skin discoloration (§5.10, §5.11)
  • Persistence after stopping (US §5.1): 'Because of the long half-life of amiodarone (15 to 142 days) and its active metabolite desethylamiodarone (14 to 75 days), adverse reactions and drug interactions can persist for several weeks following amiodarone discontinuation'

Monitoring

  • Before starting (UK SPC §4.3 and §4.4): 'Thyroid function tests should be performed in all patients prior to therapy'; and 'Before starting amiodarone, it is recommended to perform an ECG and serum potassium measurement.'
  • Before starting (US §2): 'Obtain baseline chest x-ray, pulmonary function tests, thyroid function tests, and liver aminotransferases. Correct hypokalemia, hypomagnesemia, and hypocalcemia before initiating treatment.'
  • During treatment (UK SPC §4.4): 'Monitoring of ECG is recommended during treatment.' Discontinue 'in case of onset of 2nd or 3rd degree A-V block, sino-atrial block or bifascicular block.'
  • During treatment (US §5.2, pulmonary): 'Obtain a baseline chest X-ray and pulmonary-function tests, including diffusion capacity, when Pacerone therapy is initiated. Repeat history, physical exam, and chest X-ray every 3 to 6 months'.
  • Long-term supervision (UK SPC §4.4): 'Because these reactions may be delayed, patients on long-term treatment should be carefully supervised. As undesirable effects are usually dose related the minimum effective maintenance dose should be given.'
  • Maintenance dose review (UK SPC §4.2): 'The maintenance dose should be regularly reviewed, especially where this exceeds 200 mg daily.'
  • Implanted devices (UK SPC §4.4): 'Amiodarone may increase the defibrillation threshold and/or pacing threshold in patients with an implantable cardioverter defibrillator or a pacemaker, which may adversely affect the efficacy of the device. Regular tests are recommended to ensure the proper function of the device after initiation of treatment'.
  • Elderly (UK SPC §4.2): 'Particular attention should be paid to monitoring thyroid function.'
  • Perioperative (UK SPC §4.4): 'Before surgery, the anaesthetist should be informed that the patient is taking amiodarone.'
  • Concomitant ciclosporin (US §7): 'Monitor cyclosporine drug levels and renal function with concomitant use.' Concomitant negative chronotropes (digoxin, beta blockers, verapamil, diltiazem, clonidine, ivabradine): 'Monitor heart rate.'

Clinical monograph

How it works

It mainly blocks cardiac potassium channels to prolong the action potential and refractory period, with additional sodium and calcium channel blocking and beta-adrenergic antagonist actions.

Prescribing in practice

  • Cumulative thyroid, hepatic, pulmonary and ocular toxicity together with QT prolongation mandates baseline checks, periodic monitoring and avoidance of unnecessary QT-prolonging combinations.
  • The extremely long half-life means drug interactions, including with warfarin and digoxin, continue for weeks after discontinuation.
  • The intravenous route may cause profound hypotension and venous irritation, so dilute appropriately and prefer central administration for continued infusion.

Monitoring

Check thyroid and liver function before treatment and periodically thereafter, with ECG monitoring and chest or eye review where clinically indicated.

Counselling the patient

  • Protect skin from sunlight to reduce photosensitivity reactions.
  • Report new cough, breathlessness, visual disturbance or signs of an over- or under-active thyroid.
  • Avoid grapefruit juice and inform other prescribers about long-lasting interactions.

Evidence & guidelines

Use is supported by NICE guidance on arrhythmia management and resuscitation algorithms, with MHRA communications underlining the need for organ-toxicity monitoring.

Reference: NICE NG196 (Atrial fibrillation, 2021 updated 2024); ESC Guidelines on AF (2020 updated 2024); MHRA Drug Safety Update (amiodarone thyroid, 2015); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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