Respiratory Medications

Overview of Respiratory Pharmacology

• Objective: This comprehensive overview of respiratory medications is based on the textbook Pharmacology Clear & Simple, 5th Edition by Watkins & Blades.
• Instructors: Professor LeGros and Professor DiCicco.
• Learning Outcomes:
  • Describe the function of the respiratory system in the exchange of oxygen ($O_2$) and carbon dioxide ($CO_2$) between the lungs and the blood.
  • Discuss the mechanisms and actions of various drug classes, including:
    • Mast cell stabilizers
    • Bronchodilators
    • Anticholinergics
    • Antihistamines
    • Expectorants
    • Leukotriene modifiers
    • Beta-adrenergic agonists

Anatomy and Physiology of the Pulmonary System

• Respiration: A continuous process of inhaling oxygen ($O_2$) and exhaling carbon dioxide ($CO_2$), which is a metabolic waste product.
• Site of Exchange: This occurs at the alveolar level. Alveoli are tiny air sacs deep within the lungs where gases cross into and out of the bloodstream.
• Primary Muscle of Breathing: The diaphragm is the central muscle driving respiration.
  • Inspiration: The diaphragm contracts and flattens, increasing thoracic volume and drawing oxygen-rich air in through the nose and mouth.
  • Expiration: The diaphragm and chest wall muscles relax, reducing lung volume and pushing air rich in $CO_2$ out through the airway.
• Structural Pathway: Air is channeled from the upper airway through the trachea, bronchi, and bronchioles to reach the alveoli.
• Brain Regulation: The brainstem continuously monitors and regulates the rate and depth of breathing based on blood $CO_2$ and $O_2$ levels to maintain homeostasis.
• Dyspnea: Defined as difficulty breathing. It is caused by conditions such as asthma, tuberculosis (TB), Chronic Obstructive Pulmonary Disease (COPD), or other diseases that impair airflow or gas exchange.

Questions & Discussion

• Clicker Question: Where does the exchange of $O_2$ and $CO_2$ take place?
  • Options:
    • A. Bronchi: Large airways branching from the trachea into each lung.
    • B. Trachea: The windpipe connecting the larynx to the bronchi.
    • C. Alveoli: Tiny air sacs at the end of the bronchioles deep in the lungs.
    • D. Diaphragm: The primary muscle driving breathing mechanics.
  • Answer: C. Alveoli. Their extremely thin walls and rich capillary network allow $O_2$ to diffuse into the blood and $CO_2$ to diffuse out. They are the critical site of gas exchange.

Respiratory Illnesses: Viral vs. Bacterial

• Upper Respiratory Illnesses:
  • Examples: Common cold, tonsillitis, sinusitis.
  • Etiology: Primarily viral.
  • Treatment Goal: Symptom management to support the patient while the immune system responds. Antibiotics are not effective against viruses.
• Lower Respiratory Illnesses:
  • Examples: Bronchitis and pneumonia.
  • Etiology: More commonly bacterial.
  • Clinical Significance: These are more difficult to treat and carry a higher risk of morbidity if treatment is delayed. Prompt diagnosis and antibiotic therapy are essential.

Mast Cell Stabilizers (Prophylactic Therapy)

• Mechanism of Action: Prevent allergens from binding to mast cells (specialized white blood cells). By blocking this trigger, they prevent the release of histamine and other inflammatory substances.
• Indication: Used to prevent or reduce the frequency of asthma attacks.
• Emergency Warning: These do not help during an acute asthma attack. They are strictly preventive (prophylactic).
• Key Drug: Cromolyn sodium (Intal).
• Administration Routes:
  • Metered-dose inhaler (MDI)
  • Nebulizer
  • Intranasal spray
• Patient Education: Must be used on a scheduled, regular basis. Identify a separate rescue inhaler for acute episodes.

Leukotriene Modifiers (Non-bronchodilators)

• Indication: Used for bronchoconstriction and bronchospasm in chronic asthma and COPD.
• Mechanism of Action: Relaxes bronchial smooth muscle; some agents block muscarinic receptors.
• Naming Convention: Most end in the suffix -lukast.
• Key Drug: Montelukast.
• Administration: Inhaled or oral (PO). Intravenous (IV) administration reserved for emergencies.
• Adverse Effects:
  • Nightmares
  • Depression
  • Suicidal Ideation: Must monitor patients closely for these symptoms.
• Contraindications/Precautions:
  • Caution in patients with diabetes, heart disease, liver dysfunction, kidney dysfunction, glaucoma, and Benign Prostatic Hyperplasia (BPH).
  • Allergy Note: Ipratropium preparations may contain soy lecithin; patients with peanut allergies cannot use these.
• Patient Education:
  • Powder inhalers are for scheduled use, not rescue.
  • Rinse mouth after use.
  • Wait at least 5 minutes between using two different inhaled products.
  • Take medication in the evening.

Expectorants

• Mechanism of Action: Thin and loosen thick respiratory secretions, making it easier for the patient to cough and clear the airway.
• Key Drug: Guaifenesin (Brand names: Duratuss, Mucinex, Robitussin).
• Indications: Productive coughs associated with bronchitis, sinusitis, and upper respiratory infections.
• Administration: PO (syrup, tablet, or capsule).
• Patient Education: Encourage increased fluid intake to assist in thinning secretions. These do not suppress the cough; they facilitate it.

Bronchodilators and Beta-Adrenergic Agonists

• General Purpose: Relax bronchial smooth muscle to relieve acute bronchospasm and open airways.
• Routes of Administration:
  • Inhaled: Preferred for acute therapy; rapid onset (within minutes) and minimal systemic side effects.
  • Oral: Slower onset, longer duration; used for maintenance for those who cannot tolerate inhaled forms.
• Beta-Adrenergic Agonists (Mechanism): Stimulate Beta-2 receptor sites in bronchial smooth muscle, causing dilation.
• Naming Convention: Most end in the suffix -terol.
• Short-Acting Beta Agonists (SABA) - Rescue Agents:
  • Albuterol (Proventil, Ventolin)
  • Levalbuterol (Xopenex)
  • Isoproterenol (Isuprel)
  • Terbutaline (Brethine)
• Long-Acting Beta Agonists (LABA) - Maintenance Only:
  • Formoterol (Foradil)
  • Salmeterol (Serevent)
• Emergency Treatment: Epinephrine (Adrenalin) via subcutaneous injection for life-threatening dyspnea or anaphylaxis.
• Adverse Effects: Tachycardia and tremors.
• Interactions: Beta-adrenergic blockers negate the effects of these meds. MAOIs and tricyclic antidepressants increase the risk of angina and tachydysrhythmias.
• Patient Education: Use the beta agonist first to open the airway before using a glucocorticoid. Use with a spacer for better inhalation control.

Glucocorticoids (Corticosteroids)

• Mechanism of Action: Prevents inflammation, suppresses immune response, reduces mucus secretion, and promotes beta receptor response.
• Indication: Chronic asthma and COPD management; prophylaxis only.
• Naming Convention: Most end in the suffix -sone.
• Key Drugs: Prednisone (PO), Flovent (Inhaled), Beclomethasone, Budesonide, Flunisolide.
• Adverse Effects:
  • Hoarse voice
  • Candidiasis (oral thrush)
  • Bone loss
  • Adrenal gland suppression
• Monitoring: Diabetics (medication increases blood glucose), heart failure, hypertension, and kidney impairment.
• Contraindications: Live virus vaccines and systemic fungal infections.
• Patient Education:
  • Take daily on a schedule; Flovent is not a rescue inhaler.
  • Increase diet intake of Calcium and Vitamin D.
  • Rinse mouth after use to prevent candidiasis.
  • Avoid contact with sick individuals.

Antihistamines

• Indication: Allergic reactions, motion sickness, and insomnia.
• Mechanism of Action: Works on H2 receptors (as stated in transcript) to block histamine release in small vessels.
• Naming Convention: Most end in -dine, -mine, or -zine.
• Key Drug: Diphenhydramine.
• Adverse Effects:
  • Sedation
  • GI upset
  • Toxicity signs: Flushing, urinary retention, excitability, high fever, tachycardia, pupil dilation.
  • Extravasation at injection sites.
• Monitoring: Safety (due to sedation) and respiratory distress.

Mucolytics

• Mechanism of Action: Chemically break down the structure of mucus to reduce viscosity (liquefying thick, tenacious secretions).
• Key Drug: Acetylcysteine (Mucomyst).
• Clinical Uses:
  • Cystic Fibrosis: To clear thick, sticky mucus.
  • Acetaminophen Overdose: Acts as an antidote.
• Patient Note: Acetylcysteine has a very strong sulfur-like odor.

Oxygen Therapy

• Indication: Hypoxia (low blood oxygenation).
• Uses: Chronic COPD, acute dyspnea, carbon monoxide poisoning.
• Delivery Methods: Nasal cannula, face mask, endotracheal tube, or pediatric hoods/tents.
• Safety Precautions:
  • Oxygen is a medication that must be ordered by a provider.
  • Excess oxygen can cause retinal damage (especially in neonates) and oxygen toxicity.
  • In COPD patients, high-flow oxygen may suppress the hypoxic drive.

Key Takeaway Summary

• Mast Cell Stabilizers: Prophylactic only (e.g., Cromolyn sodium).
• Glucocorticoids: Suffix -sone. Suppress inflammation. Monitor blood glucose. Rinse mouth.
• Beta-Adrenergic Agonists: Suffix -terol. Rescue (Short-acting) vs. Maintenance (Long-acting). Use before glucocorticoids.
• Antihistamines: Suffix -dine, -mine, -zine. Block histamine. Monitor for sedation/toxicity.
• Leukotrienes: Suffix -lukast. Non-bronchodilator. Monitor for depression/suicidal ideation.
• Expectorants: Thin secretions (e.g., Guaifenesin). Increase fluids.