Bronchodilators

Bronchodilators: Overview & Classes - Airway Openers 101

• Drugs that dilate bronchi & bronchioles, decreasing airway resistance and improving airflow to the lungs.
• Mechanism: Primarily act by relaxing airway smooth muscle; some also modulate inflammation.
• Key indications: Asthma, Chronic Obstructive Pulmonary Disease (COPD).
• Major Classes:
  • β2-Adrenergic Agonists (e.g., Salbutamol, Formoterol)
  • Muscarinic Antagonists (e.g., Ipratropium, Tiotropium)
  • Methylxanthines (e.g., Theophylline)

⭐ β2-agonists are the most effective bronchodilators; they activate adenylyl cyclase, leading to increased intracellular cAMP, which causes bronchial smooth muscle relaxation. 📌 Remember "BAM" for Bronchodilator classes: Beta-agonists, Anticholinergics, Methylxanthines for quick recall during exams!

Beta-2 Agonists - Speedy Relief Crew

• MOA: Activate $\beta_2$ adrenergic receptors → $↑cAMP$ → bronchial smooth muscle relaxation & bronchodilation.
• Types & Uses:

  Feature	SABA (Short-Acting)	LABA (Long-Acting)	Ultra-LABA
  Drugs	Salbutamol, Levosalbutamol, Terbutaline	Salmeterol, Formoterol	Indacaterol, Olodaterol, Vilanterol
  Onset	<5 min	Sal: 20 min, For: 2-3 min	5-15 min
  Duration	4-6 hrs	>12 hrs	>24 hrs
  Role	Rescue (acute asthma/COPD)	Maintenance (Asthma with ICS, COPD)	Maintenance (COPD, Asthma)

• 📌 Mnemonic (SABA): "Salbutamol Alleviates Breathlessness Acutely."
• Key Side Effects: Tachycardia, palpitations, tremor, hypokalemia (monitor K+), headache.

⭐ Exam Favourite: Formoterol (LABA) has rapid onset (2-3 min), like SABAs, suiting reliever/maintenance (SMART therapy).

Antimuscarinics (Anticholinergics) - Block That Squeeze

• Mechanism: Block M3 receptors in airway smooth muscle → bronchodilation by ↓ vagal tone.

• Primary use: COPD (maintenance/relief). Adjunct in severe asthma.

• Comparison:

  Feature	SAMA (e.g., Ipratropium)	LAMA (e.g., Tiotropium)
  Onset	15-30 min	~30 min
  Duration	4-6 hrs	12-24 hrs (Tio: 24h)
  Use	Acute relief (COPD/asthma)	Maintenance (COPD, asthma)

• Key Drugs:

  • SAMA: Ipratropium bromide, Oxitropium bromide.
  • LAMA: Tiotropium, Glycopyrronium, Aclidinium, Umeclidinium.

• Side Effects: Dry mouth (common), metallic taste. Systemic effects (blurred vision, urinary retention) rare with inhaled quaternary amines.

• Caution: Narrow-angle glaucoma, BPH.

⭐ Ipratropium, a quaternary amine, has minimal systemic absorption, enhancing safety.

Methylxanthines - Old School Power

• Examples: Theophylline, Aminophylline (IV).
• MOA: Non-selective PDE inhibition (↑cAMP, ↑cGMP); Adenosine receptor antagonism; ↑HDAC activity (anti-inflammatory).
• Therapeutic Range: 10-20 mcg/mL (narrow).
• AEs: Tachycardia, arrhythmias, N/V, CNS stimulation, seizures (toxic).
  • 📌 THEO: Tremors/Tachycardia, Hyperthermia/Headache, Emesis, Overdose (seizures, arrhythmias).
• Interactions: CYP450 metabolism (many drugs affect levels; smoking ↓ levels).

  ⭐ Theophylline toxicity is precipitated by macrolides (e.g., erythromycin) and quinolones (e.g., ciprofloxacin) due to CYP1A2 inhibition.

Bronchodilator Clinical Strategy - Pick Your Player

• SABA (Salbutamol): Acute relief (SOS).
• LABA (Salmeterol, Formoterol): Chronic asthma (with ICS), COPD.
• SAMA (Ipratropium): Acute asthma/COPD (adjunct).
• LAMA (Tiotropium): COPD (mainstay), severe asthma.
• Methylxanthines (Theophylline): 3rd line, monitor levels.

⭐ Formoterol: a LABA with rapid onset, suitable for SMART therapy (Single Maintenance And Reliever Therapy) in asthma.

High‑Yield Points - ⚡ Biggest Takeaways

• SABA (e.g., Salbutamol) are first-line rescue for acute asthma attacks.
• LABA (e.g., Salmeterol) for asthma maintenance, always combined with ICS.
• Anticholinergics (e.g., Ipratropium, Tiotropium) are first-line for COPD; Ipratropium in severe acute asthma.
• Theophylline: narrow therapeutic index; watch for seizures and arrhythmias.
• Leukotriene antagonists (e.g., Montelukast) for aspirin-exacerbated respiratory disease & exercise-induced asthma.
• Omalizumab (Anti-IgE monoclonal antibody) for severe, persistent allergic asthma.
• Roflumilast (PDE-4 inhibitor) reduces COPD exacerbations in severe cases_._