Respiratory Drugs – Study Notes

Case Example – Severe Asthma

• 17 y/o with asthma, SOB, multiple nebs, no relief.

• Already had albuterol + ipratropium ×5 → still symptomatic.

• Next steps:

  • IM epinephrine (esp. if multiple nebs failed).

  • IV magnesium sulfate (smooth muscle relaxer, 2g IV over 10–15 min).

  • Consider heliox if severe/refractory.

  • Inhaled corticosteroids (ICS) even in ED for faster site-specific effect.

Asthma

• Pathophysiology: chronic inflammatory airway disease, often immunologic (histamine release, mucus, bronchoconstriction).

• Triggers: allergens, viral infection, cold air, irritants.

• Treatment goals: bronchodilation + inflammation control.

Rescue (acute)

• SABA (short-acting β₂ agonists): albuterol, levalbuterol, terbutaline.

  • Onset: minutes; last ~4h.

  • Side effects: tachycardia, tremor, hypokalemia (high doses).

  • If inhaler doesn’t last ≥3 months → poorly controlled asthma.

• Epinephrine (IM 0.3 mg 1:1000 for severe exacerbation).

  • Potent β₂ + α effects (bronchodilation + mast cell stabilization).

  • Can be IM, nebulized, rarely IV.

• Magnesium sulfate (IV) – smooth muscle relaxant for refractory cases.

Maintenance

• ICS (inhaled corticosteroids) – cornerstone therapy.

  • Reduce inflammation, mast cell activity.

  • Must rinse mouth → prevent oral candidiasis.

• LABA (long-acting β₂ agonist) – always paired with ICS in asthma.

  • Black box: ↑ mortality if LABA used without ICS.

• Systemic corticosteroids (prednisone, dexamethasone, etc.) for exacerbations.

  • Start working in 4–6h.

  • Short courses (<7 days) don’t need taper.

• Monoclonal antibodies (omalizumab, mepolizumab, etc.): for severe persistent asthma, but risk anaphylaxis.

COPD

• Types:

  • Emphysema (“pink puffers”): alveolar destruction, hyperinflation, barrel chest, gas trapping, ↓ elasticity.

  • Chronic bronchitis (“blue bloaters”): chronic cough, thick sputum, frequent infections, risk hypercapnia → rely on hypoxic drive.

Treatment

• First-line: Anticholinergics (LAMA/SAMA, e.g., ipratropium, tiotropium).

  • ↓ mucus, cause bronchodilation.

  • Often combined with β₂ agonists (DuoNeb = albuterol + ipratropium).

• SABA (albuterol, levalbuterol) for rescue.

• LABA + LAMA ± ICS for maintenance (per GOLD guidelines).

• Theophylline (rare): improves diaphragmatic contraction, but narrow therapeutic range + drug interactions.

Croup

• Viral (parainfluenza, adenovirus, RSV).

• Symptoms: stridor, barky cough.

• Red flag: stridor at rest (more severe).

• Treatment:

  • Racemic epinephrine nebulized → vasoconstriction, ↓ airway edema.

  • Observe 2–4h for rebound symptoms.

  • Not for epiglottitis.

Drug Classes & Key Points

β₂ Agonists (adrenergics)

• Short-acting: albuterol, levalbuterol, terbutaline, epinephrine.

• Long-acting: salmeterol, formoterol (maintenance only).

• Effects: bronchodilation, mast cell stabilization.

• Adverse: tachycardia, tremor, hypokalemia, paradoxical bronchospasm.

• Caution: non-selective β-blockers (e.g., propranolol) may blunt effect.

Anticholinergics (antimuscarinics)

• SAMA: ipratropium.

• LAMA: tiotropium, umeclidinium.

• ↓ mucus + mild bronchodilation.

• Mainstay in COPD.

Corticosteroids

• Inhaled (ICS): budesonide, fluticasone, beclomethasone.

  • Rinse mouth → prevent thrush.

• Systemic (oral/IV): prednisone, dexamethasone, hydrocortisone.

  • Risks: hyperglycemia, immune suppression, adrenal suppression if >7–10 days.

Other Agents

• Magnesium sulfate: smooth muscle relaxer, IV for severe asthma.

• Monoclonal antibodies (MABs): omalizumab, mepolizumab for severe asthma.

• Antihistamines:

  • 1st gen (diphenhydramine): sedating, cross BBB.

  • 2nd gen (loratadine, cetirizine, fexofenadine): less sedating, first-line for allergic rhinitis.

Stepwise Asthma Management

1. SABA PRN.

2. Low-dose ICS.

3. Low-dose ICS + LABA OR medium-dose ICS.

4. Medium-dose ICS + LABA.

5. High-dose ICS + LABA ± oral steroids/biologics.

6. Severe persistent: specialist care + biologics.

Key Exam Pearls

• Stridor at rest = severe croup.

• Refractory asthma after multiple nebs → give epinephrine or magnesium.

• ICS = cornerstone of asthma maintenance.

• LABA never without ICS in asthma.

• COPD: anticholinergics first-line; differentiate emphysema vs bronchitis.

• Always rinse mouth after ICS.

• Watch for hypokalemia with high-dose β₂ agonists.