Antihistamines
- H1 blockers for allergy/urticaria
- 2nd-gen preferred for routine daytime use
- cetirizine/loratadine/fexofenadine
- 1st-gen cross BBB → sedation + antimuscarinic
- diphenhydramine/promethazine
- Some also treat nausea/vertigo
- Avoid chronic 1st-gen use when possible
Class at a glance
- H1 blockers for allergy/urticaria
Clinical role
- 2nd-gen preferred for routine daytime use
- cetirizine/loratadine/fexofenadine
Other clinical roles
- Some also treat nausea/vertigo
Safety / monitoring
- 1st-gen cross BBB → sedation + antimuscarinic
- diphenhydramine/promethazine
- Avoid chronic 1st-gen use when possible
Self-check
- Which antihistamine generation is preferred for routine daytime use?
Second generation. - Why do first-generation antihistamines cause sedation?
They cross the BBB.
Drugs in this class (16)
Antihistamines prescription history
Animated chart of estimated U.S. prescriptions per year, H1 antihistamines (1944–2026).
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