Amiodarone

Amiodarone is an antiarrythmic agent with a complex mechanism of action and many effects.

  • K+ channel blockade in cardiac myocytes, inhibiting the slow outward current and slowing repolarisation (Class III)
  • β-blocker-like activity on SA and AV nodes, decreasing automaticity and slowing nodal conduction (Class II)
  • Ca2+ channel blocker-like activity on L-type Ca2+ channels, decreasing the slow inward Ca2+ current, increasing depolarisation time and decreasing nodal conduction (Class IV)
  • α-blocker-like activity, decreasing SVR
Property Amiodarone
Class Class III antiarrhythmic, though exhibits action from all 4 classes.
Uses VT/VF, resistant arrhythmia, ALS.
Presentation 100/200mg tablets, IV: 150mg ampoule to be reconstituted in D5W.
Route of Administration IV/PO.
Dosing IV: Load with 5mg.kg-1 over 1/24, with a further 15mg.kg-1 over the following 24/24 PO: 200mg TDS for 1/52, 200mg BD for 1/52, 200mg OD thereafter.
Absorption Poor PO absorption with bioavailability ~50%.
Distribution Highly protein bound with very high VD of ~70L.kg-1s due to accumulation in fat and muscle.
Metabolism Hepatic metabolism with inhibition of CYP3A4, to the active desmethylamiodarone.
Elimination Very long t1/2 of up to ~55 days. Biliary, skin, and lacrimal elimination, with < 5% of drug eliminated renally. Not removed by dialysis.
Resp 10% 3-year risk of pneumonitis, fibrosis, pleuritis.
CVS HR, ↓ BP, ↓ SVR, ↑ QT without risk of TDP. Irritant to peripheral veins.
CNS Mild blurring of vision from corneal deposition, sleep disturbance, vivid dreams, peripheral neuropathy.
MSK Photosensitivity, grey skin.
Endocrine Hyperthyroidism (1%) and hypothyroidism (6%).
GIT Nausea, vomiting, cirrhosis, hepatitis, and jaundice.
Other Amiodarone has potential to cause a number of drug interactions due to its inhibition of CYP3A4 and its high protein binding. A selection include: Digoxin, statins, warfarin, phenytoin, and other antiarrhythmics.
Contraindicated in porphyria.

A mnemonic for some of the rarer effects is BITCH:

  • Blue skin
  • Interstitial lung disease
  • Thyroid
  • Corneal
  • Hepatic

References

  1. Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014. Peck and hill
  2. Rang HP, Dale MM, Ritter JM, Flower RJ. Rang and Dale's Pharmacology. 6th Ed. Churchill Livingstone.
Last updated 2018-07-11

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