Updated: 10/30/2019

Inhaled Beta-Agonists

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Snapshot
  • A 22-year-old woman presents to the emergency department with shortness of breath.  She has a history of seasonal allergies and eczema.  The patient is tachypneic but is saturating well on room air.  Physical exam is notable for bilateral wheezes and poor air movement.  The patient is given albuterol and her wheezing decreases and she feels better. (Asthma)
Overview
  • One of 7 medications used for asthma aimed to reduce inflammation and obstruction 
    • corticosteroids 
    • β-agonists
    • muscarinic antagonists 
    • methylxanthines 
    • antileukotrienes 
    • omalizumab 
Introduction
  • Drugs
    • short-acting, may be used during acute exacerbation
      • albuterol and levalbuterol (β2)
        • asthma 
        • COPD
      • terbutaline (β2
        • asthma (albuterol preferred as first-line)
        • tocolysis in labor
      • metaproterenol (β2 and minor β1)
        • asthma (rarely used)
    • long-acting, prophylaxis only
      • salmeterol and formoterol (β2)
        • asthma/COPD prophylaxis (not initial management for acute flares)
  • Mechanism of action
    • β-2 agonism increases cAMP causing
      • smooth muscle relaxation improving air flow
      • tachycardia when acting on the heart
      • vasodilation when acting on the blood vessels
      • tremor, sweating, anxiety, and agitation when acting systemically
      • intracellular sequestration of potassium
    • β-1 agonism increases cAMP causing the following undesirable side effects
      • cardiac effects
        • tachycardia
        • increased contractility
        • increased cardiac output
        • could increased risk of cardiac dysrhythmias
  • Clinical use
    • asthma 
    • COPD 
    • bronchospasm from chemical irritation
    • hyperkalemia 
  • Adverse effects
    • could be harmful in bronchiolitis
    • tachycardia
    • hypokalemia 
      • can cause U-waves on ECG
    • anxiety
 

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