Amiodarone

Class III anti-arrhythmic

Mechanism

  • K+ channel blocker - prolongs cardiac action potential & delaying refractory period
    1. Delays K+ efflux
    2. Depresses Na+ influx
    3. Depresses Ca2+ influx
    4. Partial antagonism of alpha & beta receptors buy reducing number of receptors or uncoupling adenyl cyclase
  • Na+ channel blocker (class I/II antiarrhythmic)
Amiodarone net effect Rate control
Metabolism Hepatic metabolism by CYP3A4; main metabolite is desethylamiodarone, which is pharmacologically active
Elimination Distributes widely, particularly into adipose tissue and lung. Elimination is extremely prolonged in chronic therapy, in excess of 100 days. Half-life is 29 days.
Time course of action Onset of action is delayed because of the redistriution, and maximum effect (especially the Class I and Class IV effects) may take weeks to develop
Adverse effects thyroid effect - see below
photosensitivity
constipation

prescribing

  • 300mg loading over 1h (large peripheral cannula or central)
  • 900mg over 23h

the infamous thyroid effect: Amiodarone-induced thyrotoxicosis

classically explained by high iodine content
should stop amiodarone if possible

  • AIT type 1: ↑ hormone synthesis → carbimazole
  • AIT type 2: destructive thyroiditis → steroids

#anti-arrhythmics #cardio #pharmacology