Overview
This lecture introduces adrenergic sympathomimetic bronchodilators, focusing on their clinical indications, mechanisms, types, side effects, administration routes, and assessments in respiratory therapy.
Clinical Indications and Mechanism
- Adrenergic bronchodilators relax airway smooth muscle during reversible bronchospasm (e.g., asthma, bronchitis, some COPD, bronchiectasis).
- Effective only if airway obstruction is reversible and primarily due to bronchoconstriction.
- Bronchodilators do not reduce airway inflammation or mucus production—only muscle constriction.
- Beta-2 adrenergic receptor stimulation causes bronchodilation via increased intracellular cAMP.
- Alpha and beta-1 receptors can be stimulated by less specific agents, causing unwanted side effects.
Types of Adrenergic Bronchodilators
- Short-acting (SABA): Used for acute relief; examples include albuterol and levalbuterol (Zopanex).
- Long-acting (LABA): Used for maintenance; examples are salmeterol, formoterol, arformoterol.
- Ultra-short acting: Racemic epinephrine, used less frequently due to non-selectivity and side effects.
- LABAs often combined with inhaled corticosteroids for better asthma control.
Pharmacology & Chemical Structure
- Most agents are synthetic catecholamines or their derivatives, mimicking epinephrine.
- Albuterol: 50/50 mix of R and S isomers; R isomer provides bronchodilation.
- Levalbuterol: Pure R isomer but not significantly superior to albuterol and is more costly.
- Racemic epinephrine: Mixture of R and S isomers, mostly used for airway swelling due to vasoconstriction.
Administration Routes & Considerations
- Inhalation (MDI, DPI, nebulizer) is preferred for rapid onset and fewer systemic side effects.
- Oral tablets and syrups are available, but act slower and carry more side effects.
- Parenteral (subcutaneous) administration is reserved for emergencies (e.g., epinephrine for severe asthma/allergic reactions).
- Continuous nebulization can be used in severe exacerbations but increases risk for toxicity.
Side Effects & Interactions
- Side effects may include tachycardia, hypertension, tremor, CNS stimulation, hyperglycemia, hypokalemia.
- Beta blockers may antagonize bronchodilator effects; timing of administration is important.
- Overuse may lead to tolerance and decreased protection against triggers.
Assessment and Monitoring
- Monitor peak flow rates before and after treatment; aim for ~20% improvement post-treatment.
- Assess lung sounds, heart rate (should not rise >20%), and patient subjective response.
- Monitor glucose, potassium, and arterial blood gases as indicated.
- Education is essential: ensure patients know when/how to use their inhalers and understand the difference between rescue and maintenance medications.
Racemic Epinephrine Special Uses
- Primarily used for airway swelling (not bronchodilation) in cases like post-extubation stridor, croup, epiglottitis, and bronchiolitis.
- Acts as a strong alpha-adrenergic vasoconstrictor to decrease airway swelling.
Key Terms & Definitions
- Bronchospasm — Constriction of airway smooth muscle causing airflow limitation.
- Beta-2 agonist — Drug stimulating beta-2 receptors to relax bronchial smooth muscle.
- Catecholamine — Chemical class of hormones/neurotransmitters like epinephrine; basis of many bronchodilators.
- SABA (Short-Acting Beta Agonist) — Fast-acting bronchodilator for acute relief.
- LABA (Long-Acting Beta Agonist) — Prolonged-action bronchodilator for maintenance.
- Racemic — Equal mixture of two mirror-image isomers (R and S).
- cAMP (Cyclic AMP) — Intracellular molecule causing relaxation of smooth muscle.
- Peak Flow Rate — Measurement of maximum speed of exhalation, used to monitor asthma.
Action Items / Next Steps
- Watch the suggested YouTube video on bronchoconstriction.
- Review drug names, durations, and distinctions between SABA, LABA, and ultra-short-acting agents.
- Practice peak flow measurements and device technique.
- Read assigned textbook sections on adrenergic bronchodilators.