What is All of the following are inotropic agents except: March 2011 and explain in detail?
Ans. B: Amiodarone Effects of amiodarone includes depression of automaticity of sinus, atria and AV node; prolongation of ERP (effective refractory period) of myocardial cells, AV nodes and abnormal pathway; slowing the conduction in AV node and specialized conducting tissue. Amiodarone It is an antiarrhythmic agent used for various types of tachyarrhythmias (fast forms of irregular hea beat), both ventricular and supraventricular (atrial) arrhythmias. Amiodarone is categorized as a class III antiarrhythmic agent, and 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 potassium channel blocker-like actions on the SA and AV nodes, increases the refractory period sodium- and potassium-channel effects, and slows intra-cardiac conduction of the cardiac action potential, sodium-channel effects. Amiodarone resembles thyroid hormone, and its binding to the nuclear thyroid receptor might contribute to some of its pharmacologic and toxic actions. * Because amiodarone has a low incidence of pro-arrhythmic effects, it has been used both in the treatment of acute life-threatening arrhythmias as well as the chronic suppression of arrhythmias. It is useful both in supraventricular arrhythmias and ventricular arrhythmias. Individuals who are pregnant or may become pregnant are strongly advised to not take amiodarone. Since amiodarone can be expressed in breast milk, women taking amiodarone are advised to stop nursing. It is contraindicated in individuals with sinus nodal bradycardia, atrioventricular block, and second or third degree hea block who do not have an aificial pacemaker. Individuals with baseline depressed lung function should be monitored closely if amiodarone therapy is to be initiated. The injection should not be given to neonates, because the benzyl alcohol it contains may cause the fatal "gasping syndrome". Amiodarone can worsen the cardiac arrhythmia brought on by Digitalis toxicity. Not to be given with Lidocaine increases risk of asystole Amiodarone is extensively metabolized in the liver by cytochrome P450 3A4, and can affect the metabolism of numerous other drugs. It interacts with digoxin, warfarin, phenytoin and others. The major metabolite of amiodarone is desethylamiodarone (DEA), which also has antiarrhythmic propeies. The metabolism of amiodarone is inhibited by grapefruit juice, leading to elevated serum levels of amiodarone. Doses of digoxin should be halved in individuals taking amiodarone. Amiodarone potentiates the action of warfarin. Individuals taking both of these medications should have their warfarin dose halved and their anticoagulation status (measured as prothrombin time (PT) and international normalized ratio (INR)) measured more frequently. Amiodarone inhibits the action of the cytochrome P450 isozyme family. This reduces the clearance of many drugs, including the following: ? - Cyclosporine - Digoxin - Flecainide - Procainamide - Quinidine - Sildenafil - Simvastatin - Theophylline - Warfarin Excretion is primarily hepatic and biliary with almost no elimination the renal route and it is not dialyzable. Elimination half-life average of 58 days (ranging from 25-100 days There is 10-50% transfer of amiodarone and DEA in the placenta as well as presence in breast milk. Accumulation of amiodarone and DEA occurs in adipose tissue and highly perfused organs (i.e. liver, lungs), therefore, if an individual was taking amiodarone on a chronic basis, if it is stopped it will remain in the system for weeks to months. The most serious reaction that is due to amiodarone is interstitial lung disease. Both under- and overactivity of the thyroid may occur on amiodarone treatment. Corneal micro-deposits (Corneal veicillata, also called voex keratopathy) are almost universally present (over 90%) in individuals taking amiodarone for at least 6 months. These deposits typically do not cause any symptoms. Abnormal liver enzyme results are common in patients on amiodarone. Much rarer are jaundice, hepatomegaly, and hepatitis Low-dose amiodarone has been repoed to cause pseudo-alcoholic cirrhosis. Long-term administration of amiodarone is associated with a blue-grey discoloration of the skin. Individuals taking amiodarone may become more sensitive to the harmful effects of UV-A light. Long-term administration of amiodarone has been associated with peripheral neuropathies. Amiodarone is sometimes responsible for epididymitis, a condition of the scrotum normally associated with bacterial infections but which can also occur as a non-bacterial inflammatory condition. It tends to resolve if amiodarone is stopped. Some cases of gynecomastia have been repoed with men on amiodarone