Drug Groups

approved; investigational

Description

An antianginal and antiarrhythmic drug. It increases the duration of ventricular and atrial muscle action by inhibiting Na,K-activated myocardial adenosine triphosphatase. There is a resulting decrease in heart rate and in vascular resistance. [PubChem]

Indication

Intravenously, for initiation of treatment and prophylaxis of frequently recurring ventricular fibrillation and hemodynamically unstable ventricular tachycardia in patients refractory to other therapy. Orally, for the treatment of life-threatening recurrent ventricular arrhythmias such as recurrent ventricular fibrillation and recurrent hemodynamically unstable ventricular tachycardia.

Pharmacology

Amiodarone belongs to a class of drugs called Vaughan-Williams Class III antiarrhythmic agents. It is used in the treatment of a wide range of cardiac tachyarhthmias, including both ventricular and supraventricular (atrial) arrhythmias. After intravenous administration in man, amiodarone relaxes vascular smooth muscle, reduces peripheral vascular resistance (afterload), and slightly increases cardiac index. Amiodarone prolongs phase 3 of the cardiac action potential. It has numerous other effects however, including actions that are similar to those of antiarrhythmic classes Ia, II, and IV. Amiodarone shows beta blocker-like and calcium channel blocker-like actions on the SA and AV nodes, increases the refractory period via sodium- and potassium-channel effects, and slows intra-cardiac conduction of the cardiac action potential, via sodium-channel effects.

Toxicity

Intravenous, mouse: LD₅₀ = 178 mg/kg. Some side effects have a significant mortality rate: specifically, hepatitis, exacerbation of asthma and congestive failure, and pneumonitis.

Affected Organisms

Biotransformation

Amiodarone is extensively metabolized in the liver via CYP2C8 (under 1% unchanged in urine), and can effect the metabolism of numerous other drugs. The major metabolite of amiodarone is desethylamiodarone (DEA), which also has antiarrhythmic properties. The metabolism of amiodarone is inhibited by grapefruit juice, leading to elevated serum levels of amiodarone.

Absorption

Slow and variable (about 20 to 55% of an oral dose is absorbed).

Half Life

58 days (range 15-142 days)

Protein Binding

>96%

Elimination

Amiodarone is eliminated primarily by hepatic metabolism and biliary excretion and there is negligible excretion of amiodarone or DEA in urine.

Clearance

* 90-158 mL/h/kg [Healthy with a single dose IV (5 mg/kg over 15 min)]
* 100 mL/h/kg [Normal subjects > 65 yrs]
* 150 mL/h/kg [younger subjects]
* 220 and 440 mL/h/kg [patients with VT and VF]

References

External Links