Isoprenaline, or isoproterenol (brand name: Isoprenaline Macure), is a

medication A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...

used for the treatment of

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), heart block, and rarely for

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 ...

. It is a non-selective β adrenoceptor agonist that is the isopropylamine analog of

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 ...

(adrenaline).

Medical uses

It is used to treat heart block and episodes of

Adams–Stokes syndrome Stokes–Adams syndrome or Adams–Stokes syndrome is a periodic fainting spell in which there is intermittent complete heart block or other high-grade arrhythmia that results in loss of spontaneous circulation and inadequate blood flow to the bra ...

that are not caused by

ventricular tachycardia Ventricular tachycardia (V-tach or VT) is a fast heart rate arising from the lower chambers of the heart. Although a few seconds of VT may not result in permanent problems, longer periods are dangerous; and multiple episodes over a short period ...

or fibrillation, in emergencies for

cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possi ...

until electric shock can be administered, for bronchospasm occurring during anesthesia, and as an adjunct in the treatment of

hypovolemic shock Hypovolemic shock is a form of shock caused by severe hypovolemia (insufficient blood volume or extracellular fluid in the body). It could be the result of severe dehydration through a variety of mechanisms or blood loss. Hypovolemic shock is a ...

septic shock Septic shock is a potentially fatal medical condition that occurs when sepsis, which is organ injury or damage in response to infection, leads to dangerously low blood pressure and abnormalities in cellular metabolism. The Third International C ...

, low cardiac output (hypoperfusion) states, congestive heart failure, and cardiogenic shock. It is also used to prevent

Torsades de Pointes ''Torsades de pointes, torsade de pointes'' or ''torsades des pointes'' (TdP) (, , translated as "twisting of peaks") is a specific type of abnormal heart rhythm that can lead to sudden cardiac death. It is a polymorphic ventricular tachycardia t ...

in patients with long QT refractory to magnesium and to treat patients with intermittent Torsades de Pointes refractory to treatment with magnesium. Historically, it was used to treat asthma via metered aerosol or nebulizing devices; it was also available in sublingual, oral, intravenous, and intramuscular formulations. The U.S. National Asthma Education and Prevention Program Expert Panel recommends against its use as a nebulizer for acute bronchoconstriction. Isoprenaline can also ameliorate the impairment of intestinal stem cells mediated by β₂-adrenoreceptors after chemotherapy.

Contraindications

It should not be used in people with tachyarrhythmias (except in special circumstances), tachycardia or heart block caused by digitalis poisoning, ventricular arrhythmias which require inotropic therapy, or with

angina Angina, also known as angina pectoris, is chest pain or pressure, usually caused by insufficient blood flow to the heart muscle (myocardium). It is most commonly a symptom of coronary artery disease. Angina is typically the result of obstr ...

Adverse effects

Adverse effects of isoprenaline include nervousness, headache, dizziness, nausea, visual blurring, tachycardia,

palpitations Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart. Symptoms include a rap ...

, angina, Adams-Stokes attacks,

pulmonary edema Pulmonary edema, also known as pulmonary congestion, is excessive liquid accumulation in the tissue and air spaces (usually alveoli) of the lungs. It leads to impaired gas exchange and may cause hypoxemia and respiratory failure. It is due ...

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 ...

hypotension Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the di ...

, ventricular arrhythmias, tachyarrhythmias, difficulty breathing, sweating, mild tremors, weakness, flushing, and

pallor Pallor is a pale color of the skin that can be caused by illness, emotional shock or stress, stimulant use, or anemia, and is the result of a reduced amount of oxyhaemoglobin and may also be visible as pallor of the conjunctivae of the eyes o ...

. Isoproterenol has been reported to cause insulin resistance leading to diabetic ketoacidosis.

Pharmacology

The adverse effects of isoprenaline are also related to the drug's cardiovascular effects. Isoprenaline can produce

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal ( ...

(an elevated

heart rate Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...

), which predisposes people who take it to

cardiac arrhythmia Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adult ...

Pharmacodynamics

Isoprenaline is a β₁ and β₂ adrenoreceptor agonist and has almost no activity on

alpha adrenergic receptor 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 ...

s. Its agonist effects at

TAAR1 Trace amine-associated receptor 1 (TAAR1) is a trace amine-associated receptor (TAAR) protein that in humans is encoded by the ''TAAR1'' gene. TAAR1 is an intracellular amine-activated and G protein-coupled receptor (GPCR) that is primarily ex ...

provide it with pharmacodynamic effects that resemble those of the endogenous

trace amine Trace amines are an endogenous group of trace amine-associated receptor 1 (TAAR1) agonists – and hence, monoaminergic neuromodulators – that are structurally and metabolically related to classical monoamine neurotransmitters. Compared to th ...

s, like

tyramine Tyramine ( ) (also spelled tyramin), also known under several other names, is a naturally occurring trace amine derived from the amino acid tyrosine. Tyramine acts as a catecholamine releasing agent. Notably, it is unable to cross the blood ...

.
Table 1: EC₅₀ values of different agonists at hTAAR1, hADRB1 and hADRB2.
Isoprenaline's effects on the

cardiovascular system The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

(non-selective) relate to its actions on cardiac β₁ receptors and β₂ receptors on smooth muscle within the

tunica media The tunica media ( New Latin "middle coat"), or media for short, is the middle tunica (layer) of an artery or vein. It lies between the tunica intima on the inside and the tunica externa on the outside. Artery Tunica media is made up of smooth ...

of arterioles. Isoprenaline has positive inotropic and chronotropic effects on the heart. β₂ adrenoceptor stimulation in arteriolar smooth muscle induces vasodilation. Its inotropic and chronotropic effects elevate systolic

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure ...

, while its vasodilatory effects tend to lower diastolic blood pressure. The overall effect is to decrease

mean arterial pressure In medicine, the mean arterial pressure (MAP) is an average blood pressure in an individual during a single cardiac cycle. MAP is altered by cardiac output and systemic vascular resistance. Testing Mean arterial pressure can be measured direc ...

due to the β₂ receptors' vasodilation. The isopropylamine group in isoprenaline makes it selective for β receptors. The free

catechol Catechol ( or ), also known as pyrocatechol or 1,2-dihydroxybenzene, is a toxic organic compound with the molecular formula . It is the ''ortho'' isomer of the three isomeric benzenediols. This colorless compound occurs naturally in trace amoun ...

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...

groups keep it susceptible to enzymatic metabolism.

Pharmacokinetics

The plasma half-life for isoproterenol is approximately two to five minutes. It is degraded enzymatically via catechol O-methyltransferase (COMT) primarily in the liver and excreted in the urine as sulfated conjugates.Szymanski MW, Singh DP. Isoproterenol. pdated 2022 Sep 27 In: StatPearls nternet Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526042/

Chemistry

It is structurally related to

History

It was first approved in the US in 1947. Between 1963 and 1968 in England, Wales, Scotland, Ireland, Australia, and New Zealand there was an increase in deaths among people using isoprenaline to treat asthma. This was attributed to overdose: the inhalers produced in that area were dispensing five times the dosage dispensed by inhalers produced in the US and Canada, where the deaths were not observed.

Society and culture

Brands

As of June 2017, isoprenaline was marketed under many brand names worldwide and as two different salts: Aleudrina, Asthpul, Iludrin, Isomenyl, Isoprenalin, Isoprenalina, Isoprenalina, Isoprenalina, Isoprenaline, Isoprenaline Macure, Isoprénaline, Isoprénaline, Isoprenaline hydrochloride, Isoprenaline sulfate, Isoprenalinesulfaat, Isoprenalinsulfat, Isoprenalinum, Isopropydine, Isopropylnoradrenaline, Isoproterenol, Isoproterenol, Isoproterenol, Isoproterenol hydrochloride, Isoproterenol sulfate, Isuprel, Isuprel, Neo-Epinine, Neodrenal, Proternol, Saventrine, and Win 5162. It is also marketed as a combination drug with

cromoglicic acid Cromoglicic acid (INN)—also referred to as cromolyn (USAN), cromoglycate (former BAN), or cromoglicate—is traditionally described as a mast cell stabilizer, and is commonly marketed as the sodium salt sodium cromoglicate or cromolyn sodium. ...

as Frenal Compositum, in combination with pronase as Isopal P, and in combination with

atropine Atropine is a tropane alkaloid and anticholinergic medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate, and to decrease saliva production during surgery. It is typically given ...

as Stmerin D.

References

{{TAAR ligands Antiasthmatic drugs Beta1-adrenergic agonists Beta2-adrenergic agonists Catecholamines Inotropic agents TAAR1 agonists Phenylethanolamines Isopropyl compounds