Beta2-adrenergic agonist

β2-adrenergic agonists, also known as β2-adrenergic receptor agonists, are a class of drugs used to treat asthma and other pulmonary disease states.

Uses
They act on the beta2-adrenergic receptor, thereby causing smooth muscle relaxation, resulting in dilation of bronchial passages, vasodilation in muscle and liver, relaxation of uterine muscle, and release of insulin.

Findings indicate isolated human coronary arterioles and small arteries dilate to NE via beta2-receptors on smooth muscle.

Side Effects
Side-effects such as insomnia, anxiety, and tremor occur in some patients.

Delivery
All β2 agonists are available in inhaler form, either metered-dose inhalers, which aerosolize the drug, or dry powder, which can be inhaled.

Salbutamol (known as albuterol in the U.S.) also comes in a solution form for nebulization, which is more commonly used in inhalers than in emergency rooms. Salbutamol and terbutaline are also both available in oral forms. Nebuliser 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 form in severe cases of asthma, but it is more commonly used to suppress premature labor because it also relaxes uterine muscle, thereby inhibiting contractions.

Risks
On November 18, 2005, Food and Drug Administration (FDA) alerted healthcare professionals and patients that several long-acting bronchodilator medicines have been associated with possible increased risk of worsening wheezing in some people, and requested that manufacturers update warnings in their existing product labeling.

On June 29, 2006, Cornell University and Stanford University researchers reported that a meta-analysis they conducted found that "regularly inhaled beta-agonists (Orciprenaline/metaproterenol [Alupent], formoterol Foradil, Fluticasone/salmeterol [Serevent, Advair], and Salbutamol/albuterol [Proventil, Ventolin, Volmax, and others]) increased the risk of respiratory death more than twofold, compared with a placebo," while used to treat chronic obstructive pulmonary disease (COPD).

On December 11, 2008, a panel of experts convened by the Food and Drug Administration (FDA) voted to ban the drugs Serevent and Foradil from use in the treatment of asthma. It was shown that, when these two drugs are used without steroids, they increase the risks of more severe attacks. The experts said that two other much more popular asthma drugs containing long-acting beta-agonists, Advair and Symbicort, should continue to be used. The latter contains formoterol as contained in Foradil but also a steroid Budesonide.

Types
They can be divided into short-acting and long-acting beta-adrenoceptor agonist (LABA) groups:

Short-acting beta2 agonists
 generic name         (Trade Name)
 * salbutamol    (albuterol (US name), Ventolin)
 * levosalbutamol (levalbuterol (US name), Xopenex)
 * terbutaline   (Bricanyl)
 * pirbuterol    (Maxair)
 * procaterol
 * metaproterenol (Alupent)
 * fenoterol
 * bitolterol mesylate
 * ritodrine

Long-acting beta2 agonists

 * salmeterol (Serevent Diskus)
 * formoterol (Foradil, Symbicort)
 * bambuterol
 * clenbuterol

Ultra-long-acting beta2 agonists

 * indacaterol