Pharmacological Management: Short-Acting β₂-Adrenergic Agonists

Josh Akers, PharmD, BCACP, and Amy Brown, MD, MBe

Introduction

•Short-acting β₂-adrenergic agonists (SABAs) are rapid-acting bronchodilators, administered as a “rescue” medication for respiratory exacerbations that involve symptoms of cough, wheezing, dyspnea, and shortness of breath.

•The differences in response to bronchodilators between infants, children, and adults are not likely due to differences in pharmacological response but are rather due to other issues related to mechanism of airway obstruction, device delivery, or other patient-specific factors.

•SABAs are meant to be used not as chronic therapy but on an “as needed” basis to relieve symptoms.

•Available SABAs include albuterol, levalbuterol, and terbutaline.

—Albuterol is available as an oral inhalation, injection, and tablet. The most common usage in pediatrics is via oral inhalation.

—Levalbuterol is only available as an oral inhalation. It is mainly reserved for patients with heart disease or those who have adverse effects of tachycardia with the administration of albuterol.

—Terbutaline is only available as an injection solution or tablet, not as an inhalation.

Mechanism of Action and Pharmacology

•Bronchodilators work by relaxing smooth muscles in the airways and inhibiting release of rapidly acting hypersensitivity mediators from mast cells.

•SABAs selectively target β₂-adrenergic receptors, a G protein–coupled transmembrane receptor, through agonist binding.

•Selectivity for β₂ is equivalent across the available SABAs.

•Peak effect from inhalation usually occurs in 25–30 minutes.

•Duration of action is generally 4–6 hours.

•Continued stimulation by an agonist may result in desensitization that occurs within 1–2 weeks of regular administration, at which point it levels off, and there may be no further worsening over time.

•U.S. Food and Drug Administration (FDA)–approved indications for asthma and bronchospasm

—2 years of age and older: Nebulized inhalation solutions

—4 years of age and older: Hydrofluoroalkane, or HFA, metered-dose inhalers (MDIs)

—6 years of age and older: Oral tablets

•Non–FDA-approved indication for asthma and bronchospasm

—Nebulized albuterol solution is commonly used in young infants who present with onset of first-time wheeze and have a history suspicious for asthma.

—MDIs with a holding chamber and face mask are often used in children <4 years of age because of ease of use and a faster response.

—Using appropriate demonstration and teach-back techniques with patients, parents, and/or guardians can ensure appropriate use of medications.

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