Beta-2-adrenoreceptor (beta-2) agonists are drugs that act as bronchodilators. The drugs stimulate the airways in the lungs (bronchi) to open wider, permitting more air to pass.
The drugs are especially helpful to asthmatics, who can suffer from insufficient air supply to the lungs due to narrowing of the bronchi. Athletes who take beta-2 agonists can also improve their athletic performance, because of the increased infusion of air. However, this type of athletic enhancement is illegal.
Beta-2 agonists such as salbutamol, salmeterol, terbutaline, and eformoterol mimic the effects of adrenaline and noradrenaline that are naturally produced in the body. The latter drugs stimulate changes in the body such as bronchial dilation, which help prepare the body to react for action (the "fight or flight" reaction).
When beta-2 agonists enter the lung bronchi, they interact with a particular receptor on the surface of the lung tissue. It is this agonist interaction with beta-2 receptors that stimulates the expansion of the bronchi.
The drugs are typically delivered to the lungs via an inhaler, although they can be delivered via an injection, as a vapor produced by a nebulizer, as a tablet, or in syrup form.
Bronchodilation is maintained for various lengths of time, depending on the beta-2 agonist used. For example, salbutamol stimulates dilation within 30 minutes, with maximum dilation reached three or four hours later. Eformoterol acts more quickly, with dilation occurring within three minutes after application, and maximum dilation reached after one to two hours. Both agonists are long lasting, with dilation persisting for approximately 12 hours. Other beta-2 agonists produce effects for shorter time periods.
Beta-2 agonists such as salbutamol have become a concern in sports. At high doses, the drug can act as an anabolic agent to promote gain in weight, mainly in the form of muscle. However, this increased strength and the increased oxygen intake comes with a risk of health damage.
As of 2006, the World Anti-Doping Agency permits the use of select beta-2 agonists (salbutamol, salmeterol, terbutaline, and eformoterol) in athletic competition only by asthmatic athletics to prevent or treat exercise-induced asthma or bronchial constriction, and then only using inhalation. Oral and injected forms of beta-2 agonists are illegal. If levels of beta-2 agonist are detected upon testing, an athlete is required to demonstrate that the drug was used for asthma.