Adrenergic (Sympathomimetic) Bronchodilators

Clinical Indications

  • Relax airway smooth muscle in reversible obstruction
    • Asthma (acute, chronic, exercise-induced)
    • Chronic bronchitis, emphysema, bronchiectasis, other obstructive diseases
  • Racemic epinephrine:
    • Control airway bleeding during endoscopy
    • Reduce post-extubation stridor, epiglottitis, croup

Agent Classification by Duration

  • Ultrashort-acting: duration <3 h → Racemic epinephrine
  • Short-acting (SABA): duration 4–64\text{–}6 h → Albuterol, Levalbuterol
  • Long-acting (LABA): duration 12–2412\text{–}24 h → Salmeterol, Formoterol, Arformoterol, Indacaterol, Olodaterol, Vilanterol

Short-Acting “Rescue/Reliever” Agents

  • Indicated for acute reversible airflow obstruction
  • Albuterol
    • Forms: MDI, DPI, Neb, Syrup, ER tablets
    • Onset 1515 min | Peak 30–6030\text{–}60 min | Duration 5–125\text{–}12 h
  • Levalbuterol (pure RR-isomer)
    • Forms: MDI, Neb (doses 0.310.31, 0.630.63, 1.251.25 mg/33 mL; 1.251.25 mg/0.50.5 mL)
    • Less tremor & HR change vs. racemic albuterol at equivalent dose

Long-Acting “Controller” Agents

  • Provide maintenance bronchodilation & nocturnal symptom control
  • Salmeterol (DPI)
    • Onset ≈20\approx20 min | Peak 3–53\text{–}5 h | Duration 1212 h
  • Formoterol (SVN, DPI)
    • Onset ≈3\approx3 min | Duration ≤12\le12 h
    • Approved: asthma maintenance, exercise-induced bronchospasm (≥55 yr)
  • Arformoterol (SVN) – single isomer, COPD maintenance, ≤12\le12 h
  • Indacaterol (DPI), Olodaterol (Respimat) – ultra-long, ≤24\le24 h, COPD maintenance
  • Vilanterol – ultra-long; only in fixed combos (Breo, Anoro, Trelegy)

Pharmacology Highlights

  • Epinephrine: potent α & β stimulation; high side-effect profile (tachycardia, ↑BP, tremor, headache, insomnia); synthetic racemic mixture
  • Catecholamines inactivated rapidly by COMT → action 1.5–31.5\text{–}3 h; unsuitable orally; degraded by heat, light, air
  • Saligenins (e.g., albuterol) show β2_2 preference, oral effectiveness, peak 30–6030\text{–}60 min, duration 4–64\text{–}6 h
  • Salmeterol & Formoterol show in-vitro mast-cell inhibition (clinical significance unproven)

Routes of Administration

  • Inhalation: MDI, DPI, Neb, Respimat
  • Oral: tablets, syrup
  • Parenteral: injection

Continuous Nebulization of Albuterol (Severe Asthma)

  • Dose: 10–1510\text{–}15 mg/h (adult)
  • Delivery: refilled SVN, infusion pump, large-volume neb, HEART/HOPE devices
  • Monitor for toxicity

Key Adverse Effects (Class-wide)

  • Tremor, tachycardia/other cardiac effects
  • Tolerance, loss of bronchoprotection
  • CNS stimulation, fall in PaO2PaO_2, metabolic changes
  • Propellant/additive reactions, paradoxical bronchospasm