The salbutamol, terbutaline and adrenaline molecules in 3-D

The salbutamol, terbutamine, adrenaline and triamcinolone molecules - rotatable in 3 dimensions

Salbutamol (ventolin, albuterol) is a bronchodilator agent. It causes relaxation of smooth muscle in the walls of bronchioles, allowing air to flow more easily into the lungs, and as such it is inhaled by asthma sufferers in the event of wheezing attacks.

It is a β-adrenergic agonist - an agent that selectively binds to and activates beta-2 adrenergic receptors. Its molecular structure closely resembles adrenaline (epinephrine), with a ←hydroxymethyl group instead of a hydroxyl group →, and a ←tertiary butyl group instead of the methyl group→ in adrenaline. It is thought that the tertiary butyl group makes the compound more effective.

The molecule has a chiral centre, and it exists in 2 forms, coded as R and S, or - and +. Salbutamol is normally sold as a racemic mixture, i.e. equal quantities of the 2 forms (enantiomers). Only the (R)-(-)-enantiomer has the pharmacologic activity, and the other (S)-(+)-enantiomer interferes with metabolic pathways which convert and remove both forms of the drug, presumably by blocking enzyme active sites.

Salbutamol and other compounds (see below) have been subject to scrutiny in the context of cycling.
Adrenaline (Epinephrine)
Terbutaline is a similar compound to salbutamol, with a tertiary butyl sidechain and a different arrangement of hydroxyl groups on the benzene ring: this makes it a 1, 3 diol rather than a 1, 2 diol as in adrenaline.
This arrangement of hydroxyl groups means that the molecule is less susceptible to breakdown by the enzyme catechol-O-methyl transferase, so that it remains active for longer.

Like salbutamol, terbutaline is mostly used as a bronchodilator for the relief of asthma attacks. It has been implicated in producing improved performance in cycling events. Terbutaline and salbutamol may improve sporting performance by altering muscle function and enhancing power production.
Terbutaline is currently on the World Anti-Doping Agency's list of prohibited drugs. However if a Therapeutic Use Exemption (TUE) has been obtained in advance, it may be permitted for use, but only when administered by inhalation. There is some concern that it may be administered orally and remain active in the body without affecting asthma.

Triamcinolone is a corticosteroid with a very different molecular structure, closer to cholesterol but with a fluorine atom.

Other molecular models on this site


Web references

Explainer: Salbutamol, asthma, and what comes next for Froome

Terbutaline: the drug at the heart of British Cycling's week from hell

What is Triamcinolone? The banned drug that's behind Sir Bradley Wiggins' steroids scandal

Doping in sport: Drug use 'fast becoming a crisis' - Nicole Sapstead