H-1 ANTAGONISTS

H-1 ANTAGONISTS, also known as H1 blockers, are a class of drugs that inhibit histamine from acting on the H1 receptor.
These are of three types-

Classification

The list you provided includes a variety of H1-antagonists (antihistamines) and one non-antihistamine medication.
H1-antagonists are primarily used to treat allergic reactions by blocking the action of histamine, a substance in the body that causes allergic symptoms.
They can be classified into two main categories: first-generation and second-generation antihistamines.
There's also one non-antihistamine drug on the list, which I'll note separately.

These are non- sedatives.
These are the oldest H1-antihistaminergic drugs, and they are widely available and at affordable price.
They are also beneficial in the alleviation of allergy symptoms.
Usually, they are also muscarinic acetylcholine receptor (anticholinergic) antagonists of moderate to high potency.

Histamine receptor is G-protein coupled receptor
H1 receptors are coupled to Phospholipase-C and their activation leads to the formation of inositol phosphate (IP3) and diacylglycerol (DAG)
Inositol phosphate cause rapid release of ca++ ions from the endoplasmic reticulum.
DAG activates protein kinase and activates Phospholipase A2.
Now, H-1 Antagonist bind to the H1 receptor and block this receptor. So, histamine dose not bind with receptor and not give any action.

Its decreases vascular permeability.
It decreases pain, headache, hypotension
These are known for their sedative effects due to their ability to cross the blood-brain barrier. They can also cause anticholinergic side effects.

These are less likely to cause sedation or anticholinergic effects as they generally do not cross the blood-brain barrier.
Major side effect of Second-generation antagonist is sedation, drowsiness because they cross blood brain barrier.
But these second generation H1- antihistamine does not cause sedation.
They are more selective for Peripheral H1-receptor.
They are hydrophilic in nature
Mechanism and use are same as first generation but does not give their action on CNS.

Mast cell stabilisers are drugs used to treat or prevent some allergic conditions. By stabilising the cell and blocking mast cell degranulation, they stop the release of histamine and other associated mediators.
It has anti-inflammatory activity.
IgE-regulated calcium channels are blocked as a pharmacodynamic mechanism.
The histamine vesicles cannot fuse to the cell membrane and degranulate in the absence of intracellular calcium.

1. Cromolyn Sodium

Here is the diagram classifying the H1-antagonists you mentioned: