Albuterol is a selective beta2-agonist that is widely used in the prevention and treatment of reactive airway disease. It is formulated as a racemic mixture containing equal parts of the R- and S-isomers. The therapeutic activity of albuterol is due entirely to the R-isomer, whereas the S-isomer may actually have detrimental effects. Because the slowly metabolized S-isomer tends to accumulate in the body, there has been concern that chronic use of racemic albuterol might lead to loss of effectiveness and clinical deterioration, with potentially serious health and cost consequences. Levalbuterol is a formulation containing only the R-isomer of albuterol, and clinical trials have demonstrated that it offers therapeutic advantages over racemic albuterol. The cost effectiveness of levalbuterol derives mainly from reduced need for acute medical care and hospitalization.