Viewing a single comment thread. View all comments

penicilling t1_irbzl51 wrote

Reply to comment by StinkyBeer in Why do some antihistamines make you sleepy? by [deleted]

>Which drugs are first gen and second gen antihistamines?

Commonly used 1st generation antihistamines include diphenhydramine, hydroxyzine and doxylamine.

Commonly used 2nd generation antihistamines include cetirizine and loratadine.

There are 3rd generation antihistamines as well, such as levocetirizne and fexofenadine. These may have even better efficacy and fewer side effects than the 2nd.

And is there a reason to take first gen at all if second gen exists now?

Because 1st generation antihistamines cross the blood-brain barrier, they have more effects. When we are treating allergic symptoms we call these effects "side effects" or "adverse effects". However, we might utilize these effects intentionally -- these drugs can reduce nausea, reduce anxiety, cause sedation, dry up secretions, reduce intestinal spasms, reduce the side effects of other medications. They are very useful in many clinical contexts.

3

notcaffeinefree t1_irc53c9 wrote

Technically, both levocetirizne and fexofenadine are classified as second generation. While third-gen is frequently used for some of the newer antihistamines, there isn't an actual defined category yet.

1

penicilling t1_irc7dqa wrote

>both levocetirizne and fexofenadine are classified as second generation.

No.

Third generation antihistamines are metabolites or enantiomers of second generation antihistamines.

Levocetirizne is the L-enantiomer of cetirizine. Fexofenadine is a metabolite of terfenadine, another second generation antihistamine. They are third generation by definition.

1