Beta-agonists are the first-line drugs for acute asthma exacerbations because they rapidly reverse bronchoconstriction and improve airflow. They act by stimulating beta-2 receptors in the smooth muscle of the airways, causing relaxation and dilation. Beta-agonists can be administered by inhalation, nebulization, or injection. Examples of beta-agonists include albuterol, levalbuterol, and terbutaline.

Management of Acute Asthma Exacerbations | AAFP: This article states that ''Quick-relief medicines include: Albuterol (ProAir HFA, Proventil-HFA, Ventolin HFA, others). Levalbuterol (Xopenex, Xopenex HFA).''

Asthma attack - Diagnosis and treatment - Mayo Clinic: This article states that ''If you're in the yellow zone, the plan will tell you how many puffs of your quick-relief medicine to take and how often you can repeat the dose. Young children or people who have difficulty with an inhaler use a device called a nebulizer to inhale the medicine in a mist. Quick-relief medicines include: Albuterol (ProAir HFA, Proventil-HFA, Ventolin HFA, others). Levalbuterol (Xopenex, Xopenex HFA).''