Antihistamines: First and Second Generation

Pharmacologic Class: H1 receptor antagonists (antihistamines) First vs Second Generation Comparison: | Feature | 1st Generation | 2nd Generation | |---|---|---| | Agents | Diphenhydramine, chlorpheniramine | Cetirizine, loratadine, fexofenadine | | CNS penetration | High (lipophilic) | Low (poor BBB crossing) | | Sedation | Marked — primary concern | Minimal (fexofenadine = non-sedating) | | Anticholinergic effects | Significant | Minimal | | Duration | 4–6 hours | 12–24 hours (once daily) | | Use in elderly | Beers Criteria — avoid | Preferred | | OTC availability | Yes | Yes | | Primary use | Acute allergic reactions, anaphylaxis adjunct, sleep | Allergic rhinitis, urticaria, chronic allergy | Critical Nursing Safety Alert: Diphenhydramine (Benadryl) is on the Beers Criteria — a list of potentially inappropriate medications in older adults (≥65). Causes: sedation, confusion, delirium, falls, urinary retention, constipation. Avoid in elderly patients for sleep or routine allergy management. Use 2nd generation alternatives. On the exam, writers often pair stable-sounding options with unstable data—notice the mismatch before you commit. If the stem names a license or role,...