Chapter 36: Antihistamines, Decongestants, Antitussives, and Expectorants

Antihistamines function by blocking histamine at H1 receptors, thereby reducing vasodilation, mucosal secretions, and tissue edema associated with allergic responses and upper respiratory inflammation. First-generation antihistamines such as diphenhydramine, chlorpheniramine, hydroxyzine, and promethazine readily cross the blood-brain barrier and produce sedation as a common adverse effect, along with anticholinergic symptoms including dry mouth, blurred vision, and urinary retention. Second-generation nonsedating antihistamines like loratadine, cetirizine, and fexofenadine offer improved selectivity for peripheral H1 receptors, minimizing central nervous system depression while maintaining therapeutic efficacy. Decongestants address nasal congestion through multiple mechanisms: adrenergic agents such as pseudoephedrine and phenylephrine cause vasoconstriction of nasal blood vessels, intranasal corticosteroids including fluticasone and budesonide reduce local inflammatory responses, and anticholinergic agents like ipratropium decrease mucus production. However, prolonged decongestant use carries the risk of rhinitis medicamentosa, a rebound congestion phenomenon requiring nursing education about appropriate duration and dosing limitations. Antitussive medications suppress cough through different pathways: opioid antitussives including codeine and hydrocodone act centrally on the medullary cough center, while nonopioid alternatives such as dextromethorphan and benzonatate provide cough suppression with reduced respiratory depression risk. Expectorants such as guaifenesin increase respiratory tract hydration, facilitating more productive cough by thinning secretions, though clinical efficacy remains debated in literature. Throughout therapeutic application, nurses must integrate comprehensive patient assessment with medication administration, monitoring for contraindications such as glaucoma or benign prostatic hyperplasia, recognizing significant drug interactions particularly with alcohol and central nervous system depressants, and distinguishing between viral and allergic etiologies to guide appropriate therapeutic selection and patient education.