| Amiodarone Pharmacology |
| Amiodarone |
| About Amiodarone |
| Class III Antiarrhythmic Agent. |
| Mechanism of Action of Amiodarone |
| It is a long acting class-3 antiarrhythmic drug. The drug exerts it`s action by: – 1) Blocks myocardial potassium channels and thus prolongs action potential duration and reduces nonuniformity of refractoriness among different fibres. 2) Preferentially blocks inactivated Na+ channels with relatively rapid rate of channel recovery; more effective in depressing conduction in cells that are partially depolarized or have longer action potential duration. 3) Inhibits Ca2+ channels of myocardium. 4) Blocking beta adrenergic receptors noncompetitively. It prolongs action potential duration effective refractory period so that conduction is slowed and ectopic automaticity is markedly depressed but only slight effect on SA node. When used I.V. causes myocardial depression and hypotension. |
| Pharmacokinets of Amiodarone |
| Absorption: absorbed incompleately and slowly after oral administration. Distribution: Distributed widely in a protein bound form preferably in to highly perfused organs and accumulates in skeletal muscles and adipose tissue. Metabolism: Metabolized in liver in to active metabolite desethyl-Amiodarone. Excretion: Excreted mainly through bile. |
| Onset of Action for Amiodarone |
| Oral: 2days to 3 weeks, I.V.: 1 to 5 minutes |
| Duration of Action for Amiodarone |
| Weeks to months |
| Half Life of Amiodarone |
| 40 to 50 days |
| Side Effects of Amiodarone |
| 1.Bradycardia 2.Hypotension 3.Arrhythmia 4.Heart block 5.Heart failure 6.Sinus arrest 7.Asystole 8.Corneal micro deposits 9.Photosensitivity 10.Visual disturbances 11.Nausea 12.Vomiting 13.Constipation 14.Abdominal pain 15.Hepatic impairment 16.Pulmonary fibrosis 17.Pneumonitis 18.Alveolitis 19.Organizing pneumonia 20.Pleuritis 21. Hypothyroidism and hyperthyroidism 22.Pancytopenia 23.Neutropenia |
| Contra-indications of Amiodarone |
| 1.Hypersensitivity to the drug 2.Second or third degree heart block 3.Congestive Heart failure 4.Cardiogenic shock 5.Severe bradycardia 6.Severe obstructive pulmonary diseases 7.Electrolyte imbalance 8.Severe Hypotension 9.Myasthenia gravis 10.Sinus node dysfunction 11.Atrial conduction defects 12.Thyroid diseases |
| Special Precautions while taking Amiodarone |
| Use with caution in following conditions: 1.Hepatic impairment 2.Renal impairment 3.Heart failure 4.In pacemaker patients 5.Monitor thyroid and liver function during therapy 6.Along with other anti arrhythmics, beta blockers, and calcium channel blockers 7.Along with antivirals like Ritonavir is contraindicated and use with caution along with Amprenavir. |
| Pregnancy Related Information |
| Contraindicated. |
| Old Age Related Information |
| Use with caution. |
| Breast Feeding Related Information |
| Contraindicated. |
| Children Related Information |
| Use with caution |
| Indications for Amiodarone |
| 1.Atrial flutter 2.Atrial fibrillation 3.Paroxysmal supra ventricular tachycardia 4.Arrhythmias with Wolff Parkinson White syndrome 5.Ventricular tachycardia 6.Recurrent ventricular fibrillation 7.Ventricular arrhythmia not responding to other treatment 8.Hypertrophic cardiomyopathy |
| Interactions for Amiodarone |
| Anticoagulants: Hypoprothrombinemic effect enhanced requiring 30% – 50% reduction in dose. Effect persists months after discontinuation of amiodarone. Beta-Blockers & Calcium Channel Antagonists ( Verapamil & Diltiazem): Additive effect. Digoxin, procainamide, Quindine, Theophyline: Increase in serum levels leading to enhanced activity of these drugs. Hydantoins: Increase in serum levels of hydantoins with decrease in levels of amiodarone. |
| Typical Dosage for Amiodarone |
| 0.2gm 8th hourly for one week; then 12th hourly for next week. Then reduce the dosage up to minimum effective dose. |
| Schedule of Amiodarone |
| H |
| Storage Requirements for Amiodarone |
| Store below 25 degree C. in a dry place and protects from light. Keep out of reach of children. |
| Effects of Missed Dosage of Amiodarone |
| Take the missed dose as soon as noticed and if it is the time for next dose then skip the missed dose. Continue the regular schedule. Do not double the dose. |
| Effects of Overdose of Amiodarone |
| Treatment is supportive and symptomatic. Monitor and support cardiovascular and respiratory functions with haemodynamic and ECG monitoring. Reverse hypotension using positive inotropic agents such as dopamine or dobutamine or vasopressors like phenylephrine or nor epinephrine. Restore heart rate with beta adrenergic agonist like isoproterinol or artificial pacing. |