Inhaled Beta Agonists

Abstract

The β₂ adrenoreceptor is a large molecule of some 413 amino acids. The duration of stimulation of this receptor depends on where and for how long a β₂ adrenergic drug attaches itself to the β₂ adrenoreceptor. β₂ adrenergic drugs have been used for over 5,000 years, but only recently have we had the advantage of adrenergic drugs specific to the β₂ adrenoreceptor. The short-acting β₂ adrenergic drugs most frequently used include albuterol, pirbuterol, and levalbuterol. Levalbuterol, the R enantiomer of albuterol, has been described by some as a more effective bronchodilator than racemic albuterol, because it contains none of the S enantiomer. Some contend that the S isomer has pro-inflammatory properties. The 2 long-acting β₂ adrenergic drugs are salmeterol and formoterol. These drugs have a duration of 12 h and reportedly improve forced expiratory volume in the first second, quality of life, and symptoms. Some recent reports indicate that these drugs are associated with higher mortality, but several authors have registered the opinion that it is not the bronchodilator that should be questioned, but instead that the fault lies in the patient recruitment in those studies. Regardless, if these long-acting drugs are effective for a given patient, it would seem inadvisable to withdraw them, given the current state of evidence. Arformoterol tartrate, the R enantiomer of formoterol, was approved by the U.S. Food and Drug Administration in October 2006; it is available as a nebulizer solution, to be administered every 12 h. Several other long-acting R isomers and RR isomers are in the approval pipeline.