BETA-2 AGONIST - A group of medications which act to relax smooth muscle and dilate the bronchioles. These medications relieve airway obstruction which causes wheezing in conditions such as COPD, asthma, and acute allergic reactions. These medications are delivered most effectively to the body when administered via inhalation in an aerosolized form. They are also available as a powder (for inhalation) and as a syrup for oral administration. Beta adrenergic bronchodilators represent the most effective first line agent in the treatment of acute bronchospasm. Examples include (Alupent), albuterol, metaproterenol, (Proventil), and pirbuterol acetate. Most of these agents act specifically on the beta2 receptors in the lungs and do not stimulate beta1 receptors in the heart.