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Antihistamines - Coggle Diagram
Antihistamines
- Allergic conditions (rhinitis, urticaria, conjunctivitis)
- Motion sickness & nausea (first gen)
- Sedation & sleep aids (first gen)
- Appetite stimulation (Cyproheptadine)
- Serotonin syndrome antidote (Cyproheptadine)
- Histamine: from histidine, stored in mast cells, enterochromaffin cells, nerves
- Effects: bronchospasm, vasodilation, edema, itching
- Target of H1 blockers (allergy symptoms)
- Effects: gastric acid secretion, cardiac effects
- Target of H2 blockers (peptic ulcers)
- H3 & H4 (less clinical relevance)
- Sedation (mainly first gen)
- Anticholinergic (dry mouth, blurred vision, constipation)
- Orthostatic hypotension (alpha-blockade)
- Drug interactions with other CNS depressants
- First gen: short half-life, multiple daily doses
- Second gen: longer half-life, once daily
- Avoid combining with other sedatives
- Some first gen used in emergencies (injectable forms)
- First Generation (Sedating)
- Examples: Diphenhydramine, Chlorpheniramine, Promethazine, Hydroxyzine, Dimenhydrinate, Cyproheptadine
- Cross BBB → sedation, anticholinergic effects (dry mouth, blurred vision)
- Uses: allergies, motion sickness, sleep aid, nausea
- Side effects: sedation, anticholinergic, orthostatic hypotension
- Second Generation (Non-sedating)
- Examples: Cetirizine, Loratadine, Fexofenadine, Desloratadine, Olopatadine, Ketotifen, Azelastine
- Minimal BBB crossing → less sedation
- Uses: allergic rhinitis, urticaria, conjunctivitis
- Fexofenadine = least sedating
- Nasal sprays: Azelastine, Olopatadine
- Eye drops: Olopatadine, Ketotifen
- Block H1 receptors → prevent histamine effects
- Do not prevent histamine release
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