Chapter 54: Drugs Acting on the Upper Respiratory Tract

Drugs Acting on the Upper Respiratory Tract on upper respiratory tract pharmacology details various drug classes engineered to manage symptoms like cough, congestion, and inflammation, thereby ensuring efficient airflow and gas exchange. Antitussives function by suppressing the cough reflex, either centrally by acting on the medullary cough center (like codeine and dextromethorphan) or peripherally as a local anesthetic on the respiratory passages (like benzonatate); however, they are contraindicated when a patient requires coughing to clear their airways and are associated with central nervous system (CNS) adverse effects such as sedation and drowsiness. Decongestants work primarily through local vasoconstriction, which decreases blood flow and reduces secretions and edema in the nasal mucous membranes. These agents are available as topical sympathomimetics (e.g., oxymetazoline, tetrahydrozoline), which carry a significant risk of rebound congestion or rhinitis medicamentosa with prolonged use, or as oral sympathomimetics (pseudoephedrine), which are more prone to systemic adrenergic effects like increased blood pressure, anxiety, and restlessness, requiring cautious use in patients with conditions like hypertension or thyroid disease. A separate class, Topical Nasal Steroid Decongestants (e.g., fluticasone, flunisolide), achieves its effect by producing a direct local antiinflammatory response, primarily used for allergic rhinitis, though their onset is delayed, potentially taking up to three weeks for full effectiveness, and their use requires caution in patients with active infections due to suppression of the inflammatory and immune response. Antihistamines selectively block histamine-1 receptor sites to alleviate allergic responses, including seasonal rhinitis and urticaria; they are categorized into first-generation agents (like diphenhydramine), which cause significant sedation and anticholinergic effects, and second-generation, less-sedating alternatives; all antihistamine use requires avoidance in patients with a history of prolonged QT intervals due as fatal arrhythmias have occurred. Finally, Expectorants (guaifenesin) increase productive cough by reducing the viscosity and adhesiveness of respiratory tract fluids, while Mucolytics (acetylcysteine, dornase alfa) are reserved for high-risk patients with thick, tenacious secretions (such as those with cystic fibrosis or COPD) to directly break down the mucus structure. Crucial nursing considerations emphasize educating patients to avoid inadvertent overdose by reading combination over-the-counter (OTC) product labels carefully, recognizing that many agents contain the same active ingredients, and monitoring patients across the lifespan for CNS effects like confusion and dizziness.