Salbutamol

Salbutamol, also called albuterol and best known by the brand Ventolin, is a drug that widens the medium and large airways in the lungs. It works as a short-acting β2 adrenergic receptor agonist, relaxing the smooth muscle in the airways. Doctors prescribe it for asthma—including acute attacks and exercise-induced bronchoconstriction—as well as for chronic obstructive pulmonary disease (COPD). It can also lower high blood potassium levels. The World Health Organization lists it as an essential medicine.

The inhaled form, delivered via inhaler or nebuliser, typically starts working within 15 minutes and lasts two to six hours. It also comes as a pill, liquid, or intravenous solution. Common side effects include shakiness, headache, a fast heart rate, dizziness, and anxiety. More serious risks include worsening bronchospasm, irregular heartbeat, and low blood potassium. Widespread use during pregnancy and breastfeeding has not shown evidence of harm.

Salbutamol was patented in Britain in 1966 and became available there in 1969. The United States approved it for medical use in 1982. It is available as a generic medication. In 2023, it was the seventh most prescribed drug in the U.S., with 59 million prescriptions.

Beyond asthma and COPD, salbutamol is used in obstetrics: intravenous doses can relax the uterine muscle to delay premature labour. While preferred over some other agents, it has largely been replaced by nifedipine, a calcium channel blocker that works better and is tolerated more easily. It also treats acute hyperkalemia by shifting potassium into cells. Two recent studies suggest it may reduce symptoms in newborns and adolescents with myasthenia gravis and its transient neonatal form.

The most common side effects are fine tremor, anxiety, headache, muscle cramps, dry mouth, and palpitations. Others include tachycardia, arrhythmia, skin flushing, rare myocardial ischemia, and sleep or behaviour disturbances. Rare but serious allergic reactions include paradoxical bronchospasm, hives, angioedema, hypotension, and collapse. High doses or prolonged use can cause hypokalemia, especially in patients with kidney failure or those taking certain diuretics and xanthine derivatives. Metered-dose inhalers using propellants are the single biggest source of carbon emissions from NHS medicines; dry powder inhalers are a lower-carbon alternative.

Chemically, salbutamol’s tertiary butyl group makes it selective for β2 receptors on bronchial smooth muscle. Activation triggers adenylyl cyclase to convert ATP to cAMP, starting a cascade that inhibits myosin phosphorylation and lowers intracellular calcium—both needed for muscle contraction. Increased cAMP also suppresses inflammatory cells like basophils, eosinophils, and mast cells from releasing mediators and cytokines. The drug also boosts conductance of calcium and potassium channels, leading to hyperpolarisation and relaxation of the airways. Salbutamol is either filtered by the kidneys or metabolised into 4′-O-sulfate and excreted in urine.

Salbutamol is sold as a racemic mixture. The (R)-(−)-enantiomer is the active form; the (S)-(+)-enantiomer blocks metabolic pathways for itself and the active form, and its slower metabolism causes it to accumulate in the lungs, potentially triggering airway hyperreactivity and inflammation. Making a pure R-form drug is complicated because the stereochemistry is unstable—it racemises within days to weeks depending on pH. Enantiomer separation and purity control can be done with thin-layer chromatography.

The chemical synthesis often starts with a Fries rearrangement of aspirin, though many other methods exist. Salbutamol was discovered in 1966 by a team led by David Jack at the Allen and Hanburys lab in Ware, England, and launched as Ventolin in 1969. At the 1972 Munich Olympics—the first with anti-doping measures—β2 agonists were banned as stimulants. Inhaled salbutamol was prohibited then, but by 1986 it was allowed (oral forms were not). After a sharp rise in athletes using β2 agonists for asthma in the 1990s, Olympic athletes had to prove they had asthma to use inhaled salbutamol.