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 blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack ( secondary prevention). They are ...

: 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 Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad ...

- 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 Adenylate cyclase (EC 4.6.1.1, also commonly known as adenyl cyclase and adenylyl cyclase, abbreviated AC) is an enzyme with systematic name ATP diphosphate-lyase (cyclizing; 3′,5′-cyclic-AMP-forming). It catalyzes the following reaction: :A ...

. This, in turn, leads to the activation of the secondary messenger

cyclic adenosine monophosphate Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger important in many biological processes. cAMP is a derivative of adenosine triphosphate (ATP) and used for intracellular signal transd ...

(cAMP); cAMP then activates

protein kinase A In cell biology, protein kinase A (PKA) is a family of enzymes whose activity is dependent on cellular levels of cyclic AMP (cAMP). PKA is also known as cAMP-dependent protein kinase (). PKA has several functions in the cell, including regulatio ...

(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 Ghrelin (; or lenomorelin, INN) is a hormone produced by enteroendocrine cells of the gastrointestinal tract, especially the stomach, and is often called a "hunger hormone" because it increases the drive to eat. Blood levels of ghrelin are hi ...

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, ...

(slow heart rate) *

Asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...

Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which may or may not produce ...

(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, ...

Allergic reaction Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derm ...

s *

Hyperkalemia Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0mmol/L (3.5 and 5.0mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Occa ...

Beta blocker Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack ( secondary prevention). They are ...

poisoning *

Premature labor Preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. Extreme preterm is less than 28 weeks, very early preterm birth is between ...

(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 Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...

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 b ...

, increased heart rate, and

insomnia Insomnia, also known as sleeplessness, is a sleep disorder in which people have trouble sleeping. They may have difficulty falling asleep, or staying asleep as long as desired. Insomnia is typically followed by daytime sleepiness, low energy, ...

. 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 Essential tremor (ET), also called benign tremor, familial tremor, and idiopathic tremor, is a medical condition characterized by involuntary rhythmic contractions and relaxations ( oscillations or twitching movements) of certain muscle groups in ...

Hypoglycemia Hypoglycemia, also called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's triad is used to properly identify hypoglycemic episodes. It is defined as blood glucose bel ...

was also reported due to increased secretion of insulin in the body from activation of β₂ receptors. In 2013, zilpaterol, 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 Denopamine ( INN) is a cardiotonic drug which acts as a β1 adrenergic receptor agonist. It is used in the treatment of angina and may also have potential uses in the treatment of congestive heart failure Heart failure (HF), also known as c ...

* 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 e ...

(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 280px, "Samguk Sagi" Book 04. Silla's Records. In 512, Usan-guk（于山國）was Ulleungdo（鬱陵島） Usan-guk, or the State of Usan, occupied Ulleung-do and the adjacent islands during the Korean Three Kingdoms period. According to th ...

) (β₁ and β₂) * Prenalterol * 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 Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular i ...

Clenbuterol Clenbuterol is a sympathomimetic amine used by sufferers of breathing disorders as a decongestant and bronchodilator. People with chronic breathing disorders such as asthma use this as a bronchodilator to make breathing easier. It is most commonl ...

(β₁ and β₂) *

(non-selective) *

Fenoterol Fenoterol is a β adrenoreceptor agonist. It is classed as sympathomimetic β2 agonist and an inhaled bronchodilator asthma medication. Fenoterol is produced and sold by Boehringer Ingelheim as Berotec N and in combination with ipratropium as ...

* Formoterol * Isoetarine * Isoprenaline ( INN), isoproterenol (

) (β₁ and β₂) * Levosalbutamol ( INN), levalbuterol (

) * Orciprenaline ( INN), metaproterenol (

) * 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 (

) * Salmeterol * Terbutaline

Undetermined/unsorted

These agents are also listed as agonists by

MeSH A mesh is a barrier made of connected strands of metal, fiber, or other flexible or ductile materials. A mesh is similar to a web or a net in that it has many attached or woven strands. Types * A plastic mesh may be extruded, oriented, exp ...

. * Arbutamine * Befunolol * Bromoacetylalprenololmenthane * Broxaterol * Cimaterol * 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 * Mabuterol *

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

* Oxyfedrine * Ractopamine * Reproterol * Rimiterol * Tretoquinol *

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 * Zinterol

References

{{Receptor agonists and antagonists