H1-first generation such as diphenhydramine or chlorpheniramine, and hydroxyzine which can cause drowsiness, impair learning, decrease work productivity and impair psychomotor performance.
More likely to cross the blood-brain barrier, causing drowsiness.
Typically work for 4-6 hours
Often used for sleep aids due to sedating effects
More likely to cause dry mouth, blurred vision, and urinary retention.
First-generation antihistamines associated with impaired learning and school performance in children.
First-generation: Block histamine receptors throughout the body, including the brain, leading to their sedating effects.
First-generation: Taken every 4-6 hours as needed Best taken at night due to drowsiness Effects typically peak within 2 hours
H1-second generation agents have fewer central nervous system adverse effects than first generation drugs.
H1 second generation drugs include loratidine, desloratadine, fexofenadine and cetirizine.
The second-generation antihistamines have a rapid onset of action and do not cross the blood-brain barrier.
The second-generation antihistamines have minimal anticholinergic activity and less drowsiness, than first generation antihistamines.
Generally work for 24 hours
Fewer anticholinergic side effects (dry mouth, blurred vision)
Often preferred for daytime use.
The second-generation antihistamines can be used as needed for rhinitis symptoms, but they generally are more effective with continuous use.
The second-generation antihistamines can be used as needed for rhinitis symptoms, but they generally are more effective with continuous use.
Second-generation: Specifically target peripheral histamine receptors, largely avoiding brain effects.
Once daily dosing Can be taken morning or night Steady state reached after 3-5 days of use
Oral suspensions are available and ease administration and compliance in young children.
Common Uses: First-generation: – Acute allergic reactions – Sleep aids – Motion sickness – Cold/flu symptom relief – Post-operative nausea – Vertigo
Second-generation: – Seasonal allergies – Chronic hives – Year-round allergies – Pet allergies – Hay fever – Dust/mold allergies