Introduction to Respiratory Pharmacology

The respiratory system, vital for gas exchange, is susceptible to various conditions ranging from acute infections to chronic obstructive diseases. Pharmacological interventions play a crucial role in managing these disorders, improving patient comfort, and preventing disease progression. This lecture provides a comprehensive overview of key drug classes used in respiratory care, emphasizing their mechanisms of action, therapeutic effects, potential side effects, and essential nursing considerations.

Learning Objectives

By the end of this session, learners will be able to:

  • Define antitussives, nasal decongestants, bronchodilators, mucolytics, and expectorants.
  • List the drug groups used for asthma and Chronic Obstructive Pulmonary Disease (COPD).
  • Explain the therapeutic effects, indications, side effects, and nursing considerations of drugs used in the respiratory system.
  • Discuss the characteristics, examples, mechanisms of action, indications, and contraindications of anti-tubercular drugs.
  • Describe the rationale for multiple drug therapy in tuberculosis treatment.
  • Discuss appropriate nursing implications for clients receiving respiratory drugs.

Pharmacotherapy for Cough, Common Cold, and Allergic Rhinitis

These common conditions often involve symptoms such as cough, nasal congestion, and allergic reactions. Several drug classes target these specific manifestations.

Antitussives: Cough Suppressants

Antitussives are medications used to suppress coughing. They primarily act by depressing the cough center in the central nervous system (CNS) or by anesthetizing stretch receptors in the respiratory tract. It is important to note that cough is a protective mechanism, and antitussives should be used cautiously, especially when cough significantly interferes with a patient's activities of daily living (ADLs).

Narcotic Antitussives: Codeine

  • Mechanism of Action: Depresses the cough center in the CNS.
  • Side Effects: Respiratory depression, constipation, sedation, dizziness, hypotension, bradycardia, and gastrointestinal (GI) upset.
  • Contraindications: Patients with COPD and drug addiction due to the risk of respiratory depression and exacerbation of dependency.

Non-Narcotic Antitussives: Benzonatate (Tessalon)

  • Mechanism of Action: Suppresses cough reflex receptors in the respiratory tract, preventing their stimulation.
  • Side Effects: Nausea, vomiting, and hypersensitivity reactions.

Nursing Considerations for Antitussives

  • Cautious Use: Administer antitussives cautiously, only when the cough is severely disruptive.
  • Avoid CNS Depressants: Instruct patients to avoid alcohol and other CNS depressants concurrently with antitussives due to increased risk of sedation and respiratory depression.
  • Respiratory Assessment: Perform respiratory assessment before and after medication administration to evaluate cough type (productive vs. dry), frequency, and the medication's effect.
  • Sedation Awareness: Inform patients that sedation is a common side effect and advise them to avoid driving or other activities requiring alertness. Most antitussives are best taken at night.
  • Administration: Codeine can be taken with milk or food to minimize GI upset.
  • Prescription Adherence: Emphasize that these drugs should not be taken over-the-counter or without a healthcare provider's prescription.

Antihistamines: H1 Receptor Antagonists

Antihistamines are used to manage symptoms of common cold and allergic rhinitis by blocking the action of histamine, a compound released during allergic and inflammatory reactions.

Mechanism of Action and Therapeutic Effects

  • Histamine Blockade: Antihistamines block histamine's action at H1 receptor sites, thereby reducing immediate hypersensitivity reactions like sneezing and itching.
  • Anticholinergic Activity: Some antihistamines also possess anticholinergic activity, which reduces parasympathetic responses, leading to bronchodilation and decreased nasal and bronchial secretions, thereby reducing nasal congestion.

Generations of Antihistamines

  • First Generation H1 Antagonists: Characterized by greater drowsiness and anticholinergic effects. Examples include Diphenhydramine (Benadryl) and Promethazine (Phenergan).
  • Second Generation H1 Antagonists: Have less sedating effects. Examples include Fexofenadine (Allegra/Telefast) and Cetirizine (Zyrtec/Zirtec).

Side Effects (especially anticholinergic)

Common side effects, particularly with first-generation antihistamines and those with significant anticholinergic activity (e.g., Diphenhydramine), include:

  • Dry mouth (due to reduced salivary secretions).
  • Urinary retention (due to bladder sphincter spasm).
  • Constipation.
  • Hemodynamic instability, tachycardia, increased blood pressure.
  • Headache and dizziness.

Contraindications

  • Narrow-angle glaucoma.
  • Known hypersensitivity to antihistamines.
  • Prostatic hypertrophy in males.
  • Bladder neck obstruction.
  • Cardiovascular disease (CVD).

Expectorants: Facilitating Mucus Clearance

Expectorants are drugs that liquefy lower respiratory tract secretions, reduce their viscosity, and facilitate mucociliary transport, making it easier for patients to cough up sputum.

Guaifenesin

  • Mechanism of Action: Promotes the removal of mucus by thinning respiratory secretions.
  • Side Effects: Nausea, vomiting, and hypersensitivity rashes.

Mucolytics: Thinning Respiratory Secretions

Mucolytics break down the chemical structure of mucus molecules, making the mucus thinner and more easily removed by coughing.

Acetylcysteine

  • Mechanism of Action: Directly breaks down the disulfide bonds in mucus proteins, thinning secretions.
  • Administration: Can be administered via inhalation (nebulizer) or instilled directly via tracheostomy. Effects are usually seen within 1 minute, with maximum effect in 5-10 minutes.
  • Side Effects: Chest tightness, mouth and throat irritation, vomiting, and increased amount of bronchial secretions (as the thinned mucus becomes more mobilizable).

Nursing Care for Mucolytics

  • Post-Administration Care: Chest physiotherapy and suctioning are often indicated after mucolytic administration, especially for tracheostomized patients, to facilitate secretion removal.
  • Patient Counseling: Inform patients that acetylcysteine may cause a disagreeable odor, which soon dissipates.
  • Facial Cleaning: If administered by face mask or nebulizer, clean the patient's face after administration as acetylcysteine can cause stickiness.

Pharmacological Management of Obstructive Pulmonary Diseases (COPD)

Obstructive pulmonary diseases encompass a group of conditions characterized by airflow limitation, often progressive, which includes asthma, COPD, emphysema, and bronchitis.

Overview of Obstructive Diseases

These diseases are defined by obstruction and inflammation of the airways.

  • Asthma: Chronic inflammatory disorder of the airways characterized by reversible airflow obstruction.
  • COPD: Progressive airflow limitation that is not fully reversible, often due to chronic bronchitis and emphysema.
  • Emphysema: Permanent enlargement of airspaces distal to the terminal bronchioles, accompanied by destruction of their walls.
  • Bronchitis: Inflammation of the bronchial tubes, often characterized by a persistent cough with sputum production.

Pathophysiological Basis for Obstruction

Airway obstruction in these conditions is primarily due to three factors:

  1. Increased mucus production.
  2. Contraction of smooth muscles (bronchoconstriction).
  3. Inflammation of the mucosal lining.

General Pathophysiology of Obstruction

In obstructive and inflammatory airway diseases, exposure to allergens or irritants leads to mast cell activation. This activation triggers the release of various inflammatory mediators, which in turn cause bronchoconstriction, airway inflammation, and mucosal edema, collectively leading to airway narrowing and obstruction.

Classes of Drugs for Obstructive Diseases

The primary goals of pharmacotherapy for obstructive diseases are to achieve bronchodilation, reduce inflammation, and facilitate mucus clearance.

Beta-2 Adrenergic Receptor Agonists (Bronchodilators)

These drugs stimulate beta-2 receptors, primarily found in the airways, uterine wall, and vascular smooth muscles, leading to relaxation of smooth muscles and bronchodilation.

  • Mechanism of Action: Activate beta-2 receptors, causing smooth muscle relaxation in the airways, increased mucociliary transport, and reduced release of inflammatory mediators. This collectively improves ventilation.
  • Therapeutic Use: Crucial for relieving acute asthma attacks and improving airflow.
  • Side Effects: While primarily targeting beta-2 receptors, these drugs can also stimulate beta-1 receptors (found in the heart), leading to side effects:
    • Palpitations: Stimulation of cardiac beta-1 receptors can cause an increased heart rate and a sensation of strong, deep pulses.
    • Tremors: Beta-receptor stimulation of skeletal muscles can cause tremors in hands and feet.
    • Peripheral Vasodilation and Hypotension: Beta-2 activation in peripheral vasculature can lead to vasodilation and a decrease in blood pressure.
  • Examples: Salbutamol (Albuterol), Salmeterol, Terbutaline.
  • Nursing Care: Assess respiratory status for improvement, monitor Arterial Blood Gases (ABGs), monitor liver function, observe for tremors, and check cardiovascular status (heart rate, blood pressure).

Methylxanthines: Theophylline and Aminophylline

These are bronchodilators primarily used for their effects on the bronchial smooth muscles.

  • Mechanism of Action: Cause bronchodilation by relaxing bronchial smooth muscles. The exact mechanism is not fully understood but involves inhibition of phosphodiesterase, leading to increased cyclic AMP. They also enhance mucociliary transport.
  • Therapeutic Use: Used to treat acute and severe asthma attacks.

Anticholinergics

These drugs produce bronchodilation by blocking the action of acetylcholine at muscarinic receptors in the airways.

  • Mechanism of Action: Block the effect of acetylcholine on autonomic nervous system receptors, leading to bronchodilation and decreased mucus production.
  • Therapeutic Use: Effective in treating acute attacks, particularly in COPD.
  • Side Effects: Dry mouth, urinary retention, hemodynamic instability, tachycardia, increased blood pressure, constipation, and dizziness (similar to anticholinergic effects of some antihistamines).
  • Example: Ipratropium bromide (Atrovent).
  • Nursing Considerations:
    • Perform respiratory assessment.
    • Instruct patients to void before medication administration to minimize urinary retention.
    • Warn patients against spraying medication into their eyes, as it can cause blurred vision and eye pain.
    • Monitor heart rate, assess for constipation, and inquire about headaches.
    • Provide frequent mouth care and encourage adequate fluid intake to counteract dry mouth and maintain hydration.

Leukotriene Receptor Antagonists (LTRAs)

LTRAs inhibit leukotrienes, which are inflammatory mediators involved in the inflammatory process, bronchial edema, and bronchoconstriction.

  • Mechanism of Action: Inhibit leukotrienes, thereby decreasing the inflammatory process, bronchial edema, and bronchoconstriction.
  • Therapeutic Use: Often used for the management of mild to moderate asthma attacks and as an adjunct to corticosteroids for improved management.
  • Examples: Montelukast (Singulair), Zafirlukast.
  • Side Effects: Hypersensitivity reactions and GI disturbances (nausea, vomiting, constipation, diarrhea).
  • Nursing Considerations:
    • Administer 1 hour before meals or 2 hours after meals, as food can reduce drug absorption.
    • Monitor Prothrombin Time (PT) / International Normalized Ratio (INR) closely if the patient is also taking Warfarin, especially with Zafirlukast.
    • Monitor Liver Function Tests (LFTs) if the drug is used for one month or longer due to potential hepatotoxicity.

Inhaled Glucocorticoids (Corticosteroids)

Glucocorticoids are potent anti-inflammatory agents used to prevent asthma exacerbations, but they are not fast-acting for acute relief.

  • Mechanism of Action: Produce anti-inflammatory effects by reducing the production of inflammatory mediators, decreasing edema, and lowering capillary permeability.
  • Therapeutic Use: Primarily used for the prevention and long-term management of asthma exacerbations. They are not effective for symptomatic relief in acute asthma attacks.
  • Administration: Available as inhalers, oral tablets, and intravenous (IV) forms.
  • Side Effects: Abdominal distress, anorexia, immunosuppression, oral fungal infections (candidiasis/thrush), and hyperglycemia.
  • Nursing Considerations:
    • Teach patients the correct use of inhalers.
    • Advise patients not to exceed the prescribed dose or stop using the inhaler without consulting a healthcare provider.
    • Counsel patients to rinse their mouth after using the inhaler and maintain good oral hygiene to reduce the risk of oral fungal infections.
    • Observe for signs of other infections and advise patients to report any bodily infections.
    • Monitor blood glucose levels, especially if oral or IV forms are administered, due to the risk of hyperglycemia.

Mast Cell Stabilizers

These are anti-inflammatory drugs that stabilize mast cells, inhibiting the release of histamine, leukotrienes, and other inflammatory mediators responsible for the inflammatory response.

  • Mechanism of Action: Prevent the release of bronchoconstrictive and inflammatory substances from mast cells when confronted with allergens.
  • Therapeutic Use: Used for chronic asthma management but have no role in acute asthma attacks.
  • Administration: Most commonly administered via inhalation.
  • Examples: Cromolyn.
  • Side Effects: Stinging or burning of the nasal mucosa, throat irritation, and nasal congestion.

Anti-Tubercular Agents: Managing Tuberculosis (TB)

Tuberculosis (TB) is a serious infectious disease caused by Mycobacterium tuberculosis. Anti-tubercular agents are crucial for treating all forms of mycobacterial infections.

Etiology and Transmission of Tuberculosis

Mycobacterium tuberculosis commonly infects the lungs (primary site) but can also affect the brain, bones, liver, and kidneys. The bacteria are transmitted via airborne droplets expelled through coughing or sneezing by an infected individual. Inhalation of these droplets allows the bacilli to enter the body, spread through the blood and lymphatic system, and infect various organs.

Primary Anti-Tubercular Drugs (First-Line Agents)

Effective treatment for TB often involves a multidrug regimen to prevent drug resistance. The primary agents are Isoniazid, Ethambutol, Pyrazinamide, Rifampin, and Streptomycin.

Isoniazid (INH)

  • Classification: Drug of choice for TB.
  • Mechanism of Action: Inhibits the formation of fatty acids essential for the mycobacterial cell membrane, preventing its growth. It is bactericidal.
  • Pharmacokinetics: Well-absorbed from the GI tract and widely distributed in body tissues and fluids.
  • Side Effects: Potentially serious adverse effects including hepatotoxicity, renal toxicity, and peripheral neuropathy.
  • Nursing Interventions:
    • Administer Pyridoxine (Vitamin B6) concurrently with Isoniazid to prevent peripheral neuropathy.
    • Monitor liver enzymes (LFTs) and renal function tests regularly.

Rifampin (RIF)

  • Mechanism of Action: Inhibits RNA synthesis in mycobacterial cells, leading to the production of defective, non-functional proteins.
  • Therapeutic Use: Always used in combination with other anti-TB drugs to minimize the development of drug resistance.
  • Side Effects: Causes a harmless but noticeable discoloration (orange-red) of body secretions (urine, tears, saliva, sputum, perspiration, feces).
  • Nursing Interventions:
    • Explain to the patient that the discoloration of body fluids is a common, temporary, and harmless side effect that will resolve after discontinuation of the drug.

Ethambutol (EMB)

  • Mechanism of Action: Inhibits RNA synthesis and interferes with mycobacterial protein metabolism, acting as a bacteriostatic agent (stops bacterial growth).
  • Major Adverse Effect: Optic neuritis, which can lead to reduced visual acuity and an inability to differentiate between red and green. This effect is usually reversible upon discontinuation.
  • Nursing Interventions:
    • Assess the patient's visual acuity and color differentiation ability regularly.
    • Explain that the visual changes are temporary and reversible.
    • Ensure that essential items are within easy reach to prevent injury due to reduced visual ability.

Pyrazinamide (PZA)

  • Mechanism of Action: Bactericidal against actively growing mycobacteria, though its exact mechanism of action is unknown.
  • Major Adverse Effects: Hepatotoxicity, nausea, vomiting, and hyperuricemia (elevated uric acid levels), which can precipitate gout attacks. The drug competes with uric acid for elimination.
  • Nursing Interventions:
    • Monitor serum uric acid levels and LFTs regularly.
    • Administer antiemetics as needed to manage nausea and vomiting.

Streptomycin (SM)

  • Classification: An aminoglycoside antibiotic.
  • Major Adverse Effects: Nephrotoxicity (kidney damage) and ototoxicity (damage to the eighth cranial nerve, leading to hearing loss or vestibular dysfunction).
  • Nursing Interventions:
    • Monitor renal function tests (Blood Urea Nitrogen, creatinine) and auditory function tests.
    • Maintain strict intake and output (I&O) monitoring.

Conclusion: Integrated Respiratory Pharmacotherapy

Understanding respiratory pharmacology is fundamental for BSN students to provide safe and effective patient care. Each drug class, from bronchodilators to anti-tubercular agents, has specific actions, indications, and potential adverse effects that necessitate diligent nursing assessment and intervention.

Key Concepts for BSN Students

  • Antihistamines (H1 Receptor Antagonists): Block histamine action, reducing allergic reactions; first-gen cause more sedation.
  • Expectorants (e.g., Guaifenesin): Facilitate mucociliary transport by liquefying secretions.
  • Mucolytics (e.g., Acetylcysteine): Break down mucus molecules, making them thinner and easier to clear.
  • Beta-2 Adrenergic Receptor Agonists: Bronchodilation by relaxing smooth muscles, often used for acute attacks.
  • Methylxanthines (e.g., Theophylline): Bronchodilation, used for acute and severe asthma.
  • Anticholinergics (e.g., Ipratropium Bromide): Bronchodilation by blocking acetylcholine, reduces mucus.
  • Leukotriene Receptor Antagonists: Inhibit inflammatory mediators, used for mild-to-moderate asthma.
  • Inhaled Glucocorticoids: Anti-inflammatory effects, primarily for chronic management, not acute relief.
  • Mast Cell Stabilizers (e.g., Cromolyn): Stabilize mast cells to prevent mediator release, for chronic asthma.
  • Anti-Tubercular Drugs: A multi-drug regimen is crucial for treating TB, with each agent having specific mechanisms and requiring close monitoring for adverse effects (e.g., hepatotoxicity, peripheral neuropathy with INH; optic neuritis with Ethambutol; discoloration of body fluids with Rifampin; ototoxicity/nephrotoxicity with Streptomycin).