Amiodarone

Question 1

Drug class?

Answer 1

Anti-dysrythmics

Question 2

How does it work?

Answer 2

Two main properties:

1. A prolongation of the myocardial cell-action potential duration and refractory period and
2. Non-competitive α- and β-adrenergic inhibition.
   Amiodarone prolongs the duration of the action potential of all cardiac fibers.

Amiodarone increases the cardiac refractory period without influencing resting membrane potential, except in automatic cells where the slope of the prepotential is reduced, generally reducing automaticity.

Question 3

Indications?

Answer 3

• Oral amiodarone is indicated only for the treatment of severe rhythm disorders not responding to other therapies or when other treatments cannot be used.
• Tachyarrhythmia associated with Wolff-Parkinson-White syndrome.
• Atrial flutter and fibrillation when other drugs cannot be used.
• All types of tachyarrhythmias of paroxysmal nature including: supraventricular, nodal and ventricular tachycardias, ventricular fibrillation: when other drugs cannot be used.
• Tablets are used for stabilisation and long-term treatment.

Question 4

Contra-indications?

Answer 4

• Sinus bradycardia and sino-atrial heart block. In patients with severe conduction disturbances (high grade AV block, bifascicular or trifascicular block) or sinus node disease, amiodarone should be used only in conjunction with a pacemaker.
• Evidence or history of thyroid dysfunction. Thyroid function tests should be performed prior to therapy in all patients.
• The combination of amiodarone with drugs which may induce Torsades de Pointes is contra-indicated.
• Pregnancy - except in exceptional circumstances.
• Lactation

Question 5

Side-effects?

Answer 5

• Cardiac disorders - bradycardia, generally moderate and dose-related.
• Endocrine disorders - hypothyroidism, hyperthyroidism, sometimes fatal.
• Eye disorders - corneal microdeposits usually limited to the area under the pupil, which are usually only discernable by slit-lamp examinations. They may be associated with colored halos in dazzling light or blurred vision. - Corneal micro-deposits consist of complex lipid deposits and are reversible following discontinuation of treatment. The deposits are considered essentially benign and do not require discontinuation of amiodarone.
• Gastrointestinal disorders - benign gastrointestinal disorders (nausea, vomiting, dysgeusia) usually occurring with loading dosage and resolving with dose reduction.
• Hepatobiliary disorders - 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. - Acute liver disorders with high serum transaminases and/or jaundice, including hepatic failure, which are sometimes fatal.
• Neurological disorders - extrapyramidal tremor, for which regression usually occurs after reduction of dose or withdrawal. Nightmares. Sleep disorders.
• Respiratory, thoracic and mediastinal disorders - Pulmonary toxicity [hypersensitivity pneumonitis, alveolar/interstitial pneumonitis or fibrosis, pleuritis, bronchiolitis obliterans organising pneumonia (BOOP)], sometimes fatal.
• Skin and subcutaneous tissue disorders: Photosensitivity. Slate grey or bluish pigmentations of light-exposed skin, particularly the face, in case of prolonged treatment with high daily dosages; such pigmentations slowly disappear following treatment discontinuation.