Question

Why do second-generation H1 blockers cause less sedation then first-generation H1 blockers? They are less potent

Answer 1

H1 antihistamines are mostly used to treat allergic reactions and mast cell-mediated disorders. ... While the first-generation H1 antihistamines have a central effect and, thus, are also used as sedatives, second-generation H1 antihistamines have less central effects and are used primarily as antiallergenic drugs.

Answer 2

Second generation H1 blockers are lipophobic (cannot cross blood brain barrier) thats why they cause less sedation than 1st generation antihistamines.

Step-by-step explanation:

There are 2 generations of antihistaminic drugs.

1st generation

2nd generation

The 1st generation drugs are the lipophilic drugs which alongwith the antiinflammatory and antiallergic effects, are lipophilic , crosses the blood brain barrier producing CNS effects by CNS sedation while also acting on muscarinic receptors and increasing CNS sedation more.

While due to the sedation problem with 1st generation antihistamines ,2nd generation was made which are lipophobic drugs and cannot cross the blood brain barrier and also cannot cause CNS sedation and they also lack cholinergic effects.