Esmolol is a cardioselective beta₁ receptor blocker with rapid onset, a very short duration of action, and no significant intrinsic sympathomimetic or membrane stabilising activity at therapeutic dosages.

It is a class II antiarrhythmic.

Esmolol decreases the force and rate of heart contractions by blocking beta-adrenergic receptors of the sympathetic nervous system

Sympathetic nervous system

The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...

, which are found in the heart

Heart

The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

 and other organs of the body. Esmolol prevents the action of two naturally occurring substances: epinephrine

Epinephrine

Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...

 and norepinephrine

Norepinephrine

Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...

.

Dosing

Esmolol is given by slow intravenous injection

Injection (medicine)

An injection is an infusion method of putting fluid into the body, usually with a hollow needle and a syringe which is pierced through the skin to a sufficient depth for the material to be forced into the body...

. It is commonly used in patients during surgery to prevent or treat tachycardia

Tachycardia

Tachycardia comes from the Greek words tachys and kardia . Tachycardia typically refers to a heart rate that exceeds the normal range for a resting heart rate...

, and is also used in treatment of acute supraventricular tachycardia. Esmolol is also the drug of choice when aortic dissection

Aortic dissection

Aortic dissection occurs when a tear in the inner wall of the aorta causes blood to flow between the layers of the wall of the aorta and force the layers apart. The dissection typically extends anterograde, but can extend retrograde from the site of the intimal tear. Aortic dissection is a medical...

 is suspected.

Metabolism

Esmolol is rapidly hydrolyzed by plasma esterases and not by plasma cholinesterases. Esmolol's short duration of action is based on the ester

Ester

Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...

-methyl side chain which allows for quick hydrolysis. Esmolol's structure is reflected in its name, Es-molol as in ester-methyl. Plasma cholinesterases and red cell membrane acetylcholinesterase do not have any action. This metabolism results in the formation of a free acid and methanol

Methanol

Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

. The amount of methanol produced is similar to endogenous methanol production. Its elimination half-life is about 9 minutes.