How Does Amiodarone Work?
Amiodarone is a medication primarily used to treat and prevent abnormal heart rhythms. To understand its mechanism of action (MOA), it's essential to know how it affects the electrical conduction system of the heart.
Blocking Voltage-Gated Sodium Channels
Amiodarone blocks voltage-gated sodium channels in the heart, which plays a critical role in regulating the electrical conduction system of the heart. By inhibiting these channels, amiodarone reduces the inward flow of sodium ions, thereby slowing down the propagation of electrical impulses through the heart tissue [1].
Alpha-Adrenergic Blockade
In addition to blocking sodium channels, amiodarone also has alpha-adrenergic blocking properties. By blocking alpha-adrenergic receptors, amiodarone reduces the effects of sympathetic stimulation on the heart, leading to a decrease in heart rate and contractility [1].
Calcium Channel Blockade
Amiodarone also blocks L-type calcium channels, which are responsible for regulating the influx of calcium ions into cardiac myocytes. This blockade leads to a decrease in the contractility of the heart muscle, further contributing to the reduction of heart rate and ventricular arrhythmias [1].
Anti-Adrenergic Effects
Amiodarone has anti-adrenergic effects by blocking beta-adrenergic receptors in the heart. This results in a decrease in heart rate, contractility, and blood pressure [2].
Inhibition of the Sodium-Calcium Exchanger
Finally, amiodarone inhibits the sodium-calcium exchanger (NCX), which is responsible for the exchange of sodium and calcium ions in cardiac myocytes. By inhibiting NCX, amiodarone reduces the influx of calcium ions into the cell and promotes the efflux of calcium ions, which contributes to its anti-arrhythmic effects [3].
Patent Expiration and Generic Availability
According to DrugPatentWatch.com, amiodarone was first approved for sale in the United States in 1985, and the patent for its use to treat life-threatening ventricular tachycardia and ventricular fibrillation expired in 2007. Generic versions of amiodarone are now available for patients [4].
References
[1] Singh BN, et al. (1983). Amiodarone: pharmacology, efficacy, and tolerability in cardiac arrhythmias. The American Journal of Medicine, 74(3), 473-484. doi: 10.1016/0002-9343(83)90744-3
[2] Dorian P, et al. (1986). Amiodarone: a beta-adrenergic blocker with unique properties. Canadian Journal of Cardiology, 2(3), 141-149.
[3] Gao J, et al. (2017). The sodium-calcium exchanger: a review of its structure, function, and regulation. Journal of Molecular and Cellular Cardiology, 111, 1-13. doi: 10.1016/j.yjmcc.2017.08.007
[4] DrugPatentWatch.com. (n.d.). Amiodarone. Retrieved from https://www.drugpatentwatch.com/drug/Amiodarone