Beta-agonist: A bronchodilator medicine that opens the airways by relaxing the muscles around the airways that may tighten during an asthma attack or in COPD (chronic obstructive pulmonary disease). Beta-agonists can be administered by inhalers or orally. They are called "agonists" because they activate the beta-2 receptor on the muscles surrounding the airways. Activation of beta-2 receptors relaxes the muscles surrounding the airways and opens the airways. Dilating airways helps to relieve the symptoms of dyspnea (shortness of breath). Beta-2 agonists have been shown to relieve dyspnea in many asthma and COPD patients. The action of beta-2 agonists starts within minutes after inhalation and lasts for about 4 hours. Because of their quick onset of action, beta-2 agonists are especially helpful for patients who are acutely short of breath but, because of their short duration of action, several doses of beta-agonists are often necessary each day. The side effects of beta-2 agonists include anxiety, tremor, palpitations or fast heart rate, and low blood potassium.
Examples of beta-2 agonists include albuterol (Ventolin, Proventil), metaproterenol (Alupent), pirbuterol (Maxair), terbutaline (Brethaire), isoetharine (Bronkosol), and Levalbuterol (Xopenex). Beta-2 agonists with a slower onset of action but a longer period of activity such as salmeterol xinafoate (Serevent) are now available. Salmeterol has a duration of action of twelve hours and need only be taken twice a day.
Side effects: Problems that occur when treatment goes beyond the desired effect. Or problems that occur in addition to the desired therapeutic effect.
A haemorrhage from the use of too much anticoagulant (such as heparin) is a side effect caused by treatment going beyond the desired effect.
The common side effects of cancer treatment including fatigue, nausea, vomiting, decreased blood cell counts, hair loss, and mouth sores are instances of side effects that occur in addition to the desired therapeutic effect.
Drug manufacturers are required to list all known side effects of their products. When side effects of necessary medication are severe, sometimes a second medication, lifestyle change, dietary change, or other measure may help to minimize them.