Chapter 37: Antihistamines, Decongestants, Antitussives & Expectorants

Antihistamines act as histamine antagonists, specifically blocking H1 receptors to mitigate effects such as increased secretions, capillary permeability, and vasodilation that lead to allergic symptoms. These are subdivided into traditional agents, like diphenhydramine, which penetrate the CNS, causing significant sedation and anticholinergic effects, and nonsedating antihistamines, such as loratadine, which work peripherally and offer a longer duration of action with fewer CNS consequences. Nasal decongestants reduce swelling in the nasal mucosa caused by excessive secretions and inflammation. This class includes adrenergic (sympathomimetic) drugs, which constrict arterioles (e.g., oxymetazoline), and intranasal corticosteroids (e.g., fluticasone) that target the local inflammatory response. A critical caution with topical adrenergic decongestants is the risk of rebound congestion with frequent or prolonged use, necessitating the selection of oral forms or intranasal steroids to avoid this effect. Antitussives are utilized to suppress nonproductive or harmful coughs by acting directly on the cough center in the medulla. This group contains opioid antitussives (e.g., codeine), which offer potent cough suppression and drying effects but carry CNS depressant and dependency risks, and nonopioid antitussives (e.g., dextromethorphan), which are widely available over the counter and less effective but still subject to potential misuse. Lastly, expectorants, such as guaifenesin, function by thinning accumulated respiratory secretions, often through reflex stimulation of the gastrointestinal (GI) tract, thus facilitating their removal via coughing (expectoration). The nursing process emphasizes a thorough assessment of contraindications, such as avoiding adrenergic decongestants in patients with uncontrolled hypertension or glaucoma, and providing crucial patient education regarding managing sedation, mitigating anticholinergic effects, and increasing fluid intake to enhance secretion clearance.