Levalbuterol is the (R)-enantiomer of the drug substance racemic albuterol (salbutamol). Binding studies have demonstrated that (R)-albuterol binds to the beta2-adrenergic receptor with a high affinity, whereas (S)-albuterol binds with 100-fold less affinity than (R)-albuterol. Other evaluations have suggested that (R)-albuterol possesses the bronchodilatory, bronchoprotective, and ciliary-stimulatory properties of racemic albuterol, while (S)-albuterol does not contribute beneficially to the therapeutic effects of the racemate and was originally assumed to be inert. Xopenex (levalbuterol HCl) Inhalation Solution is indicated for the treatment or prevention of bronchospasm in adults, adolescents, and children 6 years of age and older with reversible obstructive airway disease.

Salmeterol is a long-acting beta2-adrenergic agonist. Although beta2-adrenoceptors are the predominant adrenergic receptors in bronchial smooth muscle and beta1-adrenoceptors are the predominant receptors in the heart, there are also beta2-adrenoceptors in the human heart comprising 10% to 50% of the total beta-adrenoceptors. The precise function of these is not yet established, but they raise the possibility that even highly selective beta2-agonists may have cardiac effects. It is FDA approved for the treatment of asthma, prevention of exercise-induced bronchospasm, maintenance treatment of chronic obstructive pulmonary disease. Common adverse reactions include musculoskeletal pain, headache, influenza, nasal/sinus congestion, pharyngitis, rhinitis, tracheitis/bronchitis, cough, throat irritation, viral respiratory infection. Salmeterol should be administered with extreme caution to patients being treated with monoamine oxidase inhibitors or tricyclic antidepressants, or within 2 weeks of discontinuation of such agents, because the action of salmeterol on the vascular system may be potentiated by these agents. Coadministration of salmeterol and ketoconazole was associated with more frequent increases in QTc duration compared with salmeterol and placebo administration.

Pirbuterol (trade name Maxair) is a short-acting β2 adrenoreceptor agonist with bronchodilating action used in the treatment of asthma. The pharmacologic effects of beta-adrenergic agonist drugs, including pirbuterol, are at least in proof attributable to stimulation through beta-adrenergic receptors of intracellular adenyl cyclase, the enzyme which catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-adenosine monophosphate (c-AMP). Increased c-AMP levels are associated with relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from cells, especially from mast cells. Pirbuterol is used in asthma for reversal of acute bronchospasm, and also as a maintenance medication to prevent future attacks. It should be used in patients 12 years of age and older with or without concurrent theophylline and/or inhaled corticosteroid. After inhalation of doses up to 800 μg (twice the maximum recommended dose) systemic blood levels of pirbuterol are below the limit of assay sensitivity (2–5 ng/ml). A mean of 51% of the dose is recovered in urine as pirbuterol plus its sulfate conjugate following administration by aerosol. Pirbuterol is not metabolized by catechol-O-methyltransferase.

Pirbuterol (trade name Maxair) is a short-acting β2 adrenoreceptor agonist with bronchodilating action used in the treatment of asthma. The pharmacologic effects of beta-adrenergic agonist drugs, including pirbuterol, are at least in proof attributable to stimulation through beta-adrenergic receptors of intracellular adenyl cyclase, the enzyme which catalyzes the conversion of adenosine triphosphate (ATP) to cyclic-adenosine monophosphate (c-AMP). Increased c-AMP levels are associated with relaxation of bronchial smooth muscle and inhibition of release of mediators of immediate hypersensitivity from cells, especially from mast cells. Pirbuterol is used in asthma for reversal of acute bronchospasm, and also as a maintenance medication to prevent future attacks. It should be used in patients 12 years of age and older with or without concurrent theophylline and/or inhaled corticosteroid. After inhalation of doses up to 800 μg (twice the maximum recommended dose) systemic blood levels of pirbuterol are below the limit of assay sensitivity (2–5 ng/ml). A mean of 51% of the dose is recovered in urine as pirbuterol plus its sulfate conjugate following administration by aerosol. Pirbuterol is not metabolized by catechol-O-methyltransferase.