Dr.S.Venkatesan MD

Amiodarone has brought a major change in the medical management of ventricular arrhythmias over  the last  few decades. It is  a powerful antiarrhytmic drug , with all class 1 -4 action  (of vaugan williams classification.) It  has   sodium , pottasium, calcium and beta blocking properties.  Hence there is no surprise, amiodarone is  aptly called a broadspectrum anti arrhythmic as it  acts  on many of the cardiac receptors .

Of course , the major action is thought to be pottasium channel blocking effect(Class 3) that prolongs the action potential duration and refractory period resulting in termination of many re entrant arrhythmias.  While , amiodarone by structure resembles thyroid hormone, takes a long time to reach the steady state plasma levels  .Oral amiodarone takes  up to a week time to exert it’s action.

If amiodarone is a slow acting drug , is it not  surprising  , Why  IV amiodarone is given in the emergency managment of  VT ?

Typically , there is difference between the mechanism of  action between  oral and IV amiodarone

The class 3 property of amiodarone ,  is a late observation following oral adminstration. QT prolongation rarely  occurs  following bolus iv amiodarone . So , VT  terminating effect is thought to be some thing , other than class 3 action. Many believe the combined beta and calcium channel blocking effect could be responsible for rapid reversion of ventricular arrhythmias. The sodium channel blocking action with fast kineticks may also contribute.

Final message.

While amiodarone is a  prototype class 3 anti arrhythmic drug,  it’s  VT terminating property  may  be ,   attibutible to other class action. mean while  , the Class 3 action is responsible for long term prevention of VT/VF .