Beta adrenergic agonists or beta agonists are medications that relax muscles of the airways, causing widening of the airways and resulting in easier breathing. They are a class of

sympathomimetic Sympathomimetic drugs (also known as adrenergic drugs and adrenergic amines) are stimulant compounds which mimic the effects of endogenous agonists of the sympathetic nervous system. Examples of sympathomimetic effects include increases in hea ...

agents, each acting upon the

beta adrenoceptors The adrenergic receptors or adrenoceptors are a class of G protein-coupled receptors that are targets of many catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) produced by the body, but also many medications like beta ...

. In general, pure beta-adrenergic agonists have the opposite function of beta blockers: beta-adrenoreceptor agonist ligands mimic the actions of both

epinephrine Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...

- and norepinephrine- signaling, in the heart and lungs, and in smooth muscle tissue; epinephrine expresses the higher affinity. The activation of β₁, β₂ and β₃ activates the enzyme, adenylate cyclase. This, in turn, leads to the activation of the secondary messenger cyclic adenosine monophosphate (cAMP); cAMP then activates protein kinase A (PKA) which phosphorylates target proteins, ultimately inducing smooth muscle relaxation and contraction of the cardiac tissue.

Function

Activation of β₁ receptors induces positive

inotropic An inotrope is an agent that alters the force or energy of muscular contractions. Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction. The term ''inotro ...

, chronotropic output of the cardiac muscle, leading to increased heart rate and blood pressure, secretion of ghrelin from the stomach, and renin release from the kidneys. Activation of β₂ receptors induces smooth muscle relaxation in the lungs, gastrointestinal tract, uterus, and various blood vessels. Increased heart rate and heart muscle contraction are associated with the β1 receptors; however, β₂ cause vasodilation in the myocardium. β3 receptors are mainly located in adipose tissue. Activation of the β₃ receptors induces the metabolism of lipids.

Medical uses

Indications of administration for β agonists include: *

Bradycardia Bradycardia (also sinus bradycardia) is a slow resting heart rate, commonly under 60 beats per minute (BPM) as determined by an electrocardiogram. It is considered to be a normal heart rate during sleep, in young and healthy or elderly adults, a ...

(slow heart rate) * Asthma * Chronic obstructive pulmonary disease (COPD) *

Heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...

* Allergic reactions * Hyperkalemia * Beta blocker poisoning * Premature labor (this is an off-label use and could be detrimental)

Side effects

Although minor compared to those of epinephrine, beta agonists usually have mild to moderate adverse effects, which include anxiety,

hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...

, increased heart rate, and insomnia. Other side effects include

headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...

s and essential tremor. Hypoglycemia was also reported due to increased secretion of insulin in the body from activation of β₂ receptors. In 2013,

zilpaterol Zilpaterol (zilpaterol hydrochloride; codenamed RU 42173) is a β2 adrenergic agonist. Under its trade name, Zilmax, it is used to increase the size of cattle and the efficiency of feeding them. Zilmax is produced by Intervet, a subsidiary of M ...

, a β agonist sold by Merck, was temporarily withdrawn due to signs of sickness in some cattle that were fed the drug.

Receptor selectivity

Most agonists of the beta receptors are selective for one or more beta-adrenoreceptors. For example, patients with low heart rate are given beta agonist treatments that are more "cardio-selective" such as dobutamine, which increases the force of contraction of the heart muscle. Patients who are suffering from chronic inflammatory lung diseases such as asthma or COPD may be treated with medication targeted to induce more smooth muscle relaxation in the lungs and less contraction of the heart, including first-generation drugs like salbutamol (albuterol) and later-generation medications in the same class. β₃ agonists are currently under clinical research and are thought to increase the breakdown of lipids in obese patients.

β₁ agonists

β₁ agonists stimulate adenylyl cyclase activity and opening of calcium channel (cardiac stimulants; used to treat cardiogenic shock, acute heart failure, bradyarrhythmias). Selected examples are: * Denopamine * Dobutamine *

Dopexamine Dopexamine is a synthetic analogue of dopamine that is administered intravenously in hospitals to reduce exacerbations of heart failure and to treat heart failure following cardiac surgery. It is not used often, as more established drugs like epi ...

(β₁ and β₂) *

Epinephrine Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...

(non-selective) * Isoprenaline ( INN), isoproterenol ( USAN) (β₁ and β₂) *

Prenalterol Prenalterol is a cardiac stimulant which acts as a β1 adrenoreceptor agonist. Synthesis Stereospecific Prenalterol exhibits adrenergic agonist activity in spite of an interposed oxymethylene group. The stereospecific synthesis devised for th ...

* Xamoterol

β₂ agonists

β₂ agonists stimulate adenylyl cyclase activity and closing of calcium channel (smooth muscle relaxants; used to treat asthma and COPD). Selected examples are: * Arformoterol *

Buphenine Buphenine (or nylidrin; trade name Arlidin) is a β2 adrenoreceptor agonist that acts as a vasodilator. It was developed as a chemical derivative of oxilofrine, and first reported in the literature in 1950. See also *Isoxsuprine Isoxsupri ...

* Clenbuterol *

(β₁ and β₂) *

(non-selective) * Fenoterol *

Formoterol Formoterol, also known as eformoterol, is a long-acting β2 agonist (LABA) used as a bronchodilator in the management of asthma and chronic obstructive pulmonary disease (COPD). Formoterol has an extended duration of action (up to 12 h) co ...

Isoetarine Isoetharine is a selective short-acting β2 adrenoreceptor agonist. It can be called the "granddaughter of adrenalin" in the line of β2 agonists that gave quick relief for bronchospasm and asthma. Epinephrine (adrenalin) was the first of thes ...

* Isoprenaline ( INN), isoproterenol ( USAN) (β₁ and β₂) *

Levosalbutamol Levosalbutamol, also known as levalbuterol, is a short-acting β2 adrenergic receptor agonist used in the treatment of asthma and chronic obstructive pulmonary disease (COPD). Evidence is inconclusive regarding the efficacy of levosalbutamol ver ...

( INN), levalbuterol ( USAN) * Orciprenaline ( INN), metaproterenol ( USAN) * Pirbuterol *

Procaterol Procaterol is an intermediate-acting β2 adrenoreceptor agonist used for the treatment of asthma. It has never been filed for FDA evaluation in the United States, where it is not marketed. The drug is readily oxidized in the presence of moisture ...

* Ritodrine *

Salbutamol Salbutamol, also known as albuterol and sold under the brand name Ventolin among others, is a medication that opens up the medium and large airways in the lungs. It is a short-acting β2 adrenergic receptor agonist which works by causing rel ...

( INN), albuterol ( USAN) *

Salmeterol Salmeterol (sold in China as Qitai) is a long-acting β2 adrenergic receptor agonist (LABA) used in the maintenance and prevention of asthma symptoms and maintenance of chronic obstructive pulmonary disease (COPD) symptoms. Symptoms of bronchos ...

* Terbutaline

Undetermined/unsorted

These agents are also listed as agonists by MeSH. * Arbutamine *

Befunolol Befunolol (INN) is a beta blocker with intrinsic sympathomimetic activity used in the management of open-angle glaucoma. It also acts as a β adrenoreceptor partial agonist In pharmacology, partial agonists are drugs that bind to and activate ...

Bromoacetylalprenololmenthane Bromoacetylalprenololmenthane (BAAM or BrAAM) is a β adrenergic receptor agonist. References Acetamides N-tert-butyl-phenoxypropanolamines Allyl compounds Beta-adrenergic agonists Organobromides Cyclohexanes {{cardiovascular-d ...

Broxaterol Broxaterol is a Beta2-adrenergic agonist, β2 adrenoreceptor agonist. It is part of a class of Drug, drugs that affect the Smooth muscle tissue, smooth muscle receptors in the body, often in use cases for respiratory disease that respond to this t ...

Cimaterol Cimaterol (INN) is a beta-adrenergic agonist. See also *Dichloroisoprenaline Dichloroisoprenaline (DCI), also known as dichloroisoproterenol, was the first beta blocker ever to be developed. It is non-selective for the β1-adrenergic and β2- ...

* Cirazoline *

Etilefrine Etilefrine is a cardiac stimulant used as an antihypotensive. It is a sympathomimetic amine of the 3-hydroxy-phenylethanolamine series used in treating orthostatic hypotension of neurological, cardiovascular, endocrine or metabolic origin. Intrav ...

* Hexoprenaline * Higenamine *

Isoxsuprine Isoxsuprine (used as isoxsuprine hydrochloride) is a drug used as a vasodilator in humans (under the trade name Duvadilan) and equines. Isoxsuprine is a β2 adrenoreceptor agonist that causes direct relaxation of uterine and vascular smooth musc ...

Mabuterol Mabuterol is a selective β2 adrenoreceptor agonist. Synthesis The halogenation of 2-(Trifluoromethyl)aniline 8-17-5(1) with iodine and sodium bicarbonate resulted in 2-Amino-5-Iodobenzotrifluoride 7760-97-9(2). Protection with acetic anhydr ...

Methoxyphenamine Methoxyphenamine (trade names ASMI, Euspirol, Orthoxine, Ortodrinex, Proasma), also known as 2-methoxy-''N''- methyl amphetamine (OMMA), is a β-adrenergic receptor agonist of the amphetamine class used as a bronchodilator. It acts as an anti ...

* Oxyfedrine *

Ractopamine Ractopamine () is an animal feed additive used to promote leanness and increase food conversion efficiency in farmed animals in several countries, but banned in others. Pharmacologically, it is a phenol-based TAAR1 agonist and β adrenoreceptor ...

Reproterol Reproterol is a short-acting β2 adrenoreceptor agonist used in the treatment of asthma. It was patented in 1965 and came into medical use in 1977. Stereochemistry Reproterol contains a stereocenter and is chiral. There are thus two enant ...

Rimiterol Rimiterol (INN/USAN) is a third-generation short-acting β2 agonist. See also *Isoprenaline Isoprenaline, or isoproterenol (brand name: Isoprenaline Macure), is a medication used for the treatment of bradycardia (slow heart rate), heart b ...

Tretoquinol Tretoquinol is a beta-adrenergic agonist. References Tetrahydroisoquinolines Catechols Pyrogallol ethers {{respiratory-system-drug-stub ...

Tulobuterol Tulobuterol (INN) is a long-acting beta2-adrenergic receptor agonist, marketed in Japan as a transdermal patch A transdermal patch is a medicated adhesive patch that is placed on the skin to deliver a specific dose of medication through ...

Zilpaterol Zilpaterol (zilpaterol hydrochloride; codenamed RU 42173) is a β2 adrenergic agonist. Under its trade name, Zilmax, it is used to increase the size of cattle and the efficiency of feeding them. Zilmax is produced by Intervet, a subsidiary of M ...

Zinterol Zinterol is a beta-adrenergic agonist. Its structure is based on soterenol (antiarrhythmic Antiarrhythmic agents, also known as cardiac dysrhythmia medications, are a group of pharmaceuticals that are used to suppress abnormally fast rhythms ...

References

{{Receptor agonists and antagonists