Respiratory Pharmacology: Bronchodilators

Sympathetic Bronchodilators (Beta-agonists)

• Mechanism: Stimulate beta-2 adrenergic receptors in airway smooth muscle, causing relaxation and bronchodilation.
• Types:
  • Short-acting beta-agonists (SABAs): Quick relief; examples include albuterol and levalbuterol.
  • Long-acting beta-agonists (LABAs): Long-term control and prevention; examples include salmeterol and formoterol.
• Onset and Duration:
  • SABAs: Rapid onset (minutes) and short duration (4-6 hours).
  • LABAs: Slower onset but longer duration (up to 12 hours or more).
• Side Effects: Tachycardia, palpitations, tremors, nervousness (due to beta-1 receptor stimulation).

Parasympathetic Bronchodilators (Anticholinergics)

• Mechanism: Block acetylcholine from binding to muscarinic receptors in airway smooth muscle, preventing bronchoconstriction.
• Types:
  • Short-acting anticholinergics: Quick relief; example is ipratropium.
  • Long-acting anticholinergics: Maintenance treatment; examples include tiotropium and umeclidinium.
• Clinical Use: Acute relief (SABAs) or maintenance therapy (LABAs and long-acting anticholinergics, particularly in chronic conditions like COPD).

Comparison of Bronchodilators

• Mechanism Differences: Sympathetic bronchodilators directly stimulate beta-2 receptors, while parasympathetic bronchodilators block acetylcholine.
• Onset and Duration: Sympathetic bronchodilators (especially SABAs) act quickly, while parasympathetic bronchodilators have a slower onset but longer duration.
• Side Effect Profiles: Sympathetic bronchodilators can cause cardiovascular side effects, while parasympathetic bronchodilators primarily cause localized effects like dry mouth.