Amiodarone contains iodine and is structurally related to thyroxine. It shows the affects of all classes i.e. class I, II, III and IV.
Mechanism of action:
Amiodarone blocks the sodium channels in inactivated state. It also blocks the calcium channels but to a less extent. It also noncompetitively inhibits α- and β- adrenoceptors.
Its dominant action is the increase in duration of action potential. It also causes an increase in effective refractory period in the atrial and ventricular muscles.
It causes an increase in PR, QRS and QT intervals.
It causes a decrease in sinus rate and AV conduction as well as systemic and coronary vasodilation.
It is not well absorbed orally. It has a prolonged half life of about 20-100 days and distributes mostly into adipose tissues. Its full effects are seen after 6 weeks of start of treatment.
It is used in
2. Premature ventricular contractions
3. Ventricular tachyarrhythmia
4. Refractory supraventricular arrhythmias
5. Arrhythmias in patients with wolf Parkinson white syndrome
It may cause gastrointestinal intolerance (nausea, vomiting, and constipation), headache, dizziness, paresthesias, pulmonary fibrosis and blue skin discoloration (due to the increased concentration of iodine in the skin).