What is Amiodarone?
Class 3 Anti Arrhytmic
Amiodarone may be an acronym for its IUPAC name (2-butyl-1-benzofuran-3-yl)-[4-[2-(diethylamino)ethoxy]-3,5-diiodophenyl]methanone, where ar is a placeholder for phenyl.
diiodo / C25H29I2NO3 – 2 iodine (rich iodine)
figure: amiodarone structure
figure: thyroxine structure
Amiodarone is rich iodine drug. Money Money Money.
High Iodine lead to Wolff–Chaikoff effect
- is a reduction in thyroid hormone levels caused by ingestion of a large amount of iodine
- autoregulatory phenomenon that inhibits organification in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid hormones into the bloodstream.
- an effective means of rejecting a large quantity of ingested iodide, and therefore preventing the thyroid from synthesizing large quantities of thyroid hormone.
figure: looks iodides inhibition on several steps
Amiodarone may cause thyroid dysfunction in patients with preexisting thyroid disease and destructive thyroiditis in patients with normal thyroid glands.
An antithyroid drug given simultaneously blocks iodine organification and prevents iodide-induced exacerbation of thyrotoxicosis. Hence, the thyrotoxicosis-induced effect of amiodarone should not preclude its use in thyrotoxic atrial fibrillation,[provided that it is given in conjunction with antithyroid agents.
But Amiodarone will convert AF to SR. Precaution to AF with unknown duration or >48 H -thrombus formation)
Amiodarone don’t look so bad. As long use with conjunction of anti thyroid drug right? So can Amiodarone be use?
Rate control: The first step in the management of atrial fibrillation, despite the cause, is to control the ventricular response.
Shirley Ooi said it too.
page 310 2nd edition
So which agent should be use?
Heart failure or non heart failure?
Non heart failure
- Beta Blocker
- propranolol has the advantage of reducing the peripheral conversion of T4 to T3; however, this effect is of minor therapeutic value, and other cardioselective agents with longer half-lives are equally effective.
- Calcium Channel Blocker
- diltiazem or verapamil, can be useful for long-term control of ventricular rate in patients in whom beta-adrenergic blockade is contraindicated.
- used cautiously, as these may cause severe hypotension and a further reduction in systemic vascular resistance that is already low in patients with thyrotoxicosis.
Hyperthyroid atrial fibrillation is typically resistant to digoxin that is caused in part by an increase in the renal clearance and apparent volume of its distribution as well as increased sympathetic and reduced vagal tone. A larger-than-usual dose of digoxin is required, which increases the risk of its toxicity. Despite these limitations, digoxin should still be considered in patients with heart failure and concomitant thyrotoxic atrial fibrillation.