H1 Antagonist - First-generation (non-selective, Classical)

First-generation (non-selective, Classical)

These are the oldest H1-antihistaminergic drugs and are relatively inexpensive and widely available. They are effective in the relief of allergic symptoms, but are typically moderately to highly potent muscarinic acetylcholine receptor (anticholinergic) antagonists as well. These agents also commonly have action at α-adrenergic receptors and/or 5-HT receptors. This lack of receptor selectivity is the basis of the poor tolerability profile of some of these agents, especially compared with the second-generation H1-antihistamines. Patient response and occurrence of adverse drug reactions vary greatly between classes and between agents within classes.

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H1 Antagonist - First-generation (non-selective, Classical) - Common Structural Features
... Two aromatic rings,connected to a central carbon,nitrogen or CO Spacer between the central X and the amine,usually 23 carbons in length,linear ... CH3 X N,R1 R2 small alkyl groups X C X CO Chirality at X can increase both the potency and selectivity for H1-receptors For maximum potency,the two aromatic rings should be orientated in different ...