AMIODARONE

CLASS 3 ANTIARRHYTHMIC

Supra ventricular & Ventricular Arrhythmias 

- Prolongs phase three of the cardiac action potential (8-24h) - increasing refractory period via Na & K channels.

- Increases duration of ventricular and atrial muscle; inhibiting Na,K-activated myocardial ATP-ase. 

SOURCES

http://www.pathophys.org/wp-content/uploads/2013/10/ActionPotential.png

Little negative inotropic activity, and little chance of pro-arrhythmias = advantageous for use in patients with heart failure

Chemically resembles thyroxine (T4), and its binding to the nuclear thyroid receptor might contribute to some of its pharmacologic and toxic actions  (am-IOD-arone = iodine)

Oral Bioavailability = 22 to 95% 

- Amiodarone is extensively metabolized in the liver by cytochrome P450 3A4.

- Interacts with digoxin, warfarin, phenytoin, and others. 

IV  and oral amiodarone have different electrophysiological properties and it may be possible to administer i.v. amiodarone to cardiovert AF in patients who are already on chronic oral treatment.

Most toxicity of amiodarone is dose-dependent and related to chronic treatment; however, it should be used with caution in patients with acute ischaemia or myocardial dysfunction, as profound hypotension may be induced by i.v. or high-dose oral loading. 

There is evidence that Magnesium Sulphate can be used synergistically with amiodarone to prevent arrhythmias*

S/E's = hypotension, bradycardia and peripheral phlebitis. 

Contraindications to IV amiodarone are bradycardia, senoatrial block, severe disturbance of conduction & 2nd/3rd AV block

Should not be used with polymorphic VT as it associated with a prolonged QT interval which is made worse with antiarrhythmic drugs.

QT interval represents electrical depolarization and repolarization of the ventricles.

Pharmacological interactions: 

- Statins = (Simvastatin >20mg can cause rhabdomyolysis)

propofology.com

Dr. David Lyness

@Gas_Craic

IV loading: 

Initially 5 mg/kg over 20–120 minutes with ECG.