I've been researching H1-antihistamines for personal reasons. And I'm trying to find out if H1-antihistamines are sorted based on pharmacology.
I understand that H1-antihistamines have up to three generations. And with each new generation, the drugs get safer and have less side effects.
According to Wikipedia, the antihistamines are also classified 5 classes based on their chemical structures.
But further research shows that each antihistamine works differently in suppressing allergic responses and possesses varying potency.
Loratadine, for example,
acts as a selective inverse agonist of peripheral histamine H1 receptors.
Loratadine also shows anti-inflammatory properties independent of H1 receptors. The effect is exhibited through suppression of the NF-κB pathway, and by regulating the release of cytokines and chemokines, thereby regulating the recruitment of inflammatory cells.
Bepotastine, on the other hand,
is a direct H1-receptor antagonist that inhibits the release of histamine from mast cells.
And Azelastine has a triple mode of action:
Anti-histamine effect, Mast-cell stabilizing effect and Anti-inflammatory effect.
When given orally, antihistamines are also absorbed in various ways.
Loratadine, according to Wikipedia,
is given orally, is well absorbed from the gastrointestinal tract, and has rapid first-pass hepatic metabolism.
Ebastine undergoes similar absorption. But other antihistamines, notably, Cetirizine and Olopatadine, do not undergo hepatic metabolism.
What I'm wondering is: Do the antihistamines from the same generation (second generation, for example) have official classifications that group different antihistamines with similar pharmacodynamics together?
I've scoured NIH medical articles and haven't been able to find such classification. But I'm unsure if I'm simply not thorough in my search or if this type of classification doesn't exist for medical professionals.