Submitted by [deleted] t3_xxa73t in askscience
notcaffeinefree t1_irc53c9 wrote
Reply to comment by penicilling in Why do some antihistamines make you sleepy? by [deleted]
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.
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.
notcaffeinefree t1_irc8ri5 wrote
They're both still H1 antagonists. Their exact method of action is slightly different, but they still target H1 receptors.
Both are listed as 2nd-gen:
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