Beta Agonists

Beta agonists are medications commonly used to treat “reactive airway disease,” or asthma. These medications stimulate the beta-2 receptors, which are found in the lungs in very small airways called alveoli. The beta-2 receptors are present in the muscles that surround the alveoli. When these muscles contract, the alveoli constrict, and less air moves through. This process is called bronchoconstriction. These alveoli have very small cross-sectional space so that even a mild constriction can significantly alter the airflow. This is what happens in an asthma exacerbation. The beta agonists relax the muscles that surround the alveoli.

In asthma, there are often triggers that cause bronchoconstriction. Common triggers are exposure to cold, stress, exercise, or allergens such as animal dander, pollen, medications, or food. It is important for anyone with asthma to learn his or her specific triggers and avoid them. Bronchoconstriction can be rapid and deadly, and sometimes beta-agonist treatment is not enough to reverse it. Asthma has an inflammatory component as well, which means that the alveoli swell and mucus is produced. Beta agonists cannot treat this aspect of asthma, and the inflammation will get worse if the asthma is left untreated or if there are repetitive exposures to triggers. In addition, continued use of beta agonists may make them less effective over time.

Any chemicals that stimulate beta receptors are considered beta agonists. Most of the medications that are designed to stimulate beta-2 receptors will also stimulate beta-1 receptors, which are found in the heart and control the heart rate. That is why beta-agonist medications usually increase the heart rate (i.e., stimulation of beta-1 receptors in the heart as an unintended consequence). Epinephrine (adrenaline), caffeine, and cocaine are some examples of beta agonists. Cold medications such as pseudo-ephedrine and some herbal supplements (such as ma huang) have beta-agonist properties. One of the most commonly used beta agonists in the treatment of asthma is albuterol. Albuterol is most often inhaled through a metered dose inhaler (MDI, or “puffer”). It is also available in pill form or inhaled in powder form.

Athletes use beta agonists to prevent or treat reactive airway disease. They are sometimes abused to increase the heart rate and get a competitive advantage. Beta agonists were previously thought to have mild anabolic (muscle building) properties, and so their use in competition was strictly prohibited. After further study, there does not appear to be any significant anabolic effect. This fact, and the [Page 149]significant rise of asthma rates worldwide, has contributed to relaxing of the restrictions on beta-agonist use in competition. Certain beta agonists such as formoterol, salbutamol, salmeterol, and terbutaline are permitted but regulated in international competition and during training. These medications are permitted to be taken by inhalation to prevent and/or treat asthma and exercise-related respiratory problems. Athletes still need documented proof that they have reactive airway disease and a prescription in order to compete while taking these medications (therapeutic use exemption).

Beta agonists have a role in treating asthma, but they must be used properly, and an athlete needs to be aware of the risks and side effects. Common side effects include jitteriness, increased heart rate, tremor, and difficulty sleeping. Beta agonists can exacerbate or cause arrhythmias (erratic and sometimes deadly irregular heartbeats).

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