(R)-(−)-salbutamol (center) and
|Trade names||Ventolin, Proventil, others|
|by mouth, inhalational, IV|
|Onset of action||<15 min (inhaled), <30 min (pill)|
|Biological half-life||3.8–6 hours|
|Duration of action||2–6 hrs|
|Chemical and physical data|
|Molar mass||239.311 g/mol|
|3D model (Jmol)|
|(what is this?)|
Salbutamol, also known as albuterol and marketed as Ventolin among other names, is a medication that opens up the medium and large airways in the lungs. It is used to treat asthma, exercise-induced bronchospasm, and chronic obstructive pulmonary disease (COPD). It may also be used to treat high blood potassium levels. It is usually used by inhaler or nebulizer but is also available as a pill and intravenous solution. Onset of action of the inhaled version is typically within 15 minutes and lasts for two to six hours.
Common side effects include shakiness, headache, fast heart rate, dizziness, and feeling anxious. Serious side effects may include worsening bronchospasm, irregular heartbeat, and low blood potassium levels. It can be used during pregnancy and breastfeeding, but safety is not entirely clear. Salbutamol is a short-acting β2 adrenergic receptor agonist which works by causing airway smooth muscles to relax.
Salbutamol was first made in 1967 in Britain. It was approved for medical use in the United States in 1982. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. It is available as a generic medication. The wholesale cost in the developing world of an inhaler which contains 200 doses is between $1.12 and $2.64 (USD) as of 2014. In the United States it is between $25 and $50 for a typical month supply.
As a β2 agonist, salbutamol also finds use in obstetrics. Intravenous salbutamol can be used as a tocolytic to relax the uterine smooth muscle to delay premature labor. While preferred over agents such as atosiban and ritodrine, its role has largely been replaced by the calcium channel blocker nifedipine, which is more effective, better tolerated and orally administered.
The most common side effects are fine tremor, anxiety, headache, muscle cramps, dry mouth, and palpitation. Other symptoms may include tachycardia, arrhythmia, flushing, myocardial ischemia (rare), and disturbances of sleep and behaviour. Rarely occurring, but of importance, are allergic reactions of paradoxical bronchospasm, urticaria, angioedema, hypotension, and collapse. High doses or prolonged use may cause hypokalaemia, which is of concern especially in patients with renal failure and those on certain diuretics and xanthine derivatives.
Structure and activity
This drug is sold as a racemic mixture. The (R)-(−)-enantiomer (CIP nomenclature) is shown in the image at right (top), and is responsible for the pharmacologic activity; the (S)-(+)-enantiomer (bottom) blocks metabolic pathways associated with elimination of itself and of the pharmacologically active enantiomer (R).
Detection after dosing
Salbutamol may be quantified in blood or plasma; practical needs for this include to confirm a diagnosis of poisoning in hospitalized patients, or to aid in a forensic investigation. As well, urinary salbutamol concentrations are frequently measured in competitive sports programs, for which a level in excess of 1000 μg/L is considered to represent abuse.
The window of detection for urine testing is on the order of just 24 hours, given the relatively short elimination half-life of the drug, estimated at between 5 and 6 hours following oral administration of 4 mg.
Society and culture
The wholesale cost of an inhaler which contains 200 doses is between $1.12 and $2.64 (USD) in the developing world as of 2014. In the United Kingdom the wholesale price of an inhaler which contains 200 doses is GB£1.50 as of 2015. In the United States a typical month supply is between $25 and $50.
In some countries compliance with the Montreal Protocol, which requires the banning of the use of ozone-layer depleting CFCs, has caused the price of inhalers to increase as much as ten-fold, as generics have been forced off the market from 2009 to 2013 by new patents obtained by pharmaceutical companies for non-CFC delivery systems.
There is no compelling evidence that salbutamol and other β2 agonists can increase performance in healthy athletes. In spite of this, salbutamol required "a declaration of Use in accordance with the International Standard for Therapeutic Use Exemptions" under the 2010 WADA prohibited list. This requirement was relaxed when the 2011 list was published to permit the use of "salbutamol (maximum 1600 micrograms over 24 hours) and salmeterol when taken by inhalation in accordance with the manufacturers’ recommended therapeutic regimen."
Another study contradicts the above findings, however. The double blind, randomised test conducted on 12 non-asthmatic athletes concluded that salbutamol had a negligible effect on endurance performance. Nevertheless, the study also showed that the drug's bronchodilating effect may have improved respiratory adaptation at the beginning of exercise.
Salbutamol has been shown to improve muscle weight in rats and anecdotal reports hypothesise that it might be an alternative to clenbuterol for purposes of fat burning and muscle gain, with multiple studies supporting this claim. Abuse of the drug may be confirmed by detection of its presence in plasma or urine, typically exceeding 1000 µg/L.
It has also been tested in a trial aimed at treatment of spinal muscular atrophy; it is speculated to modulate the alternative splicing of the SMN2 gene, increasing the amount of the SMN protein whose deficiency is regarded as a cause of the disease.
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