{{DISPLAYTITLE:Beta2-adrenergic agonist}} Beta2-adrenergic agonists, also known as adrenergic β2 receptor agonists, are a class of drugs that act on the β2 adrenergic receptor. Like other β adrenergic agonists, they cause smooth muscle relaxation. β2 adrenergic agonists' effects on smooth muscle cause dilation of bronchial passages, vasodilation in muscle and liver, relaxation of uterine muscle, and release of insulin. They are primarily used to treat asthma and other pulmonary disorders, such as Chronic obstructive pulmonary disease (COPD). Mechanism of action Activation of β adrenergic receptors leads to relaxation of smooth muscle in the lung, and dilation and opening of the airways. β adrenergic receptors are coupled to a stimulatory G protein of adenylyl cyclase. This enzyme produces the second messenger cyclic adenosine monophosphate (cAMP). In the lung, cAMP decreases calcium concentrations within cells and activates protein kinase A. Both of these changes inactivate myosin light-chain kinase and activate myosin light-chain phosphatase. In addition, β2 agonists open large conductance calcium-activated potassium channels and thereby tend to hyperpolarize airway smooth muscle cells. The combination of decreased intracellular calcium, increased membrane potassium conductance, and decreased myosin light chain kinase activity leads to smooth muscle relaxation and bronchodilation. Adverse effects Findings indicate that β2 stimulants, especially in parenteral administration such as inhalation or injection, can induce adverse effects: Tachycardia secondary to peripheral vasodilation and cardiac stimulation (Such tachycardia may be accompanied by palpitations.) Tremor, excessive sweating, anxiety, insomnia, and agitation More severe effects include paradoxical bronchospasm, hypokalemia, and in rare cases a myocardial infarction. (More severe effects, such as pulmonary edema, myocardial ischemia, and cardiac arrhythmia, are exceptional.) Overuse of β2 agonists and asthma treatment without proper inhaled corticosteroid use has been associated with an increased risk of asthma exacerbations and asthma-related hospitalizations. The excipients, in particular sulfite, could contribute to the adverse effects. Delivery All β2 agonists are available in inhaler form, either metered-dose inhalers, which aerosolize the drug, or dry powder inhalers, which dispense powder to be inhaled. Salbutamol (INN) or albuterol (USAN) and some other β2 agonists, such as formoterol, also are sold in a solution form for nebulization, which is more commonly used than inhalers in emergency rooms. Salbutamol and terbutaline are also both available in oral forms. The nebulizer form is as effective as administering the drug intravenously. In addition, several of these medications are available in intravenous forms, including both salbutamol and terbutaline. It can be used in this