Classification of Histamine Receptors ||PharmaEasyNotes ||@Pharmacy 💊


When histamine is released, the physiological effect is mediated by a specific cell surface receptor. These receptors are divided into three subtypes.


(i) H1 Receptors

It is found in smooth muscle of intestine,
Bronchi
Blood vessels
adrenal medulla and endothelial cell
Lymphocytes.

(ii) H2 receptor

It is present in the Tissues of myocardial cell and cell membranes of acid secretory cell and mediates the gastric acid Secretary action.

(iii) H3 receptor

It is a presynaptic receptor that influences the release of histamine and other neurotransmitters from neurons.

Classification

The H1 antagonists are referred first-generation Or classic antihistamines.

A First-generation antihistamines

(i) Aminoalikyl ethers
eg. Diphenylhydramine Hydrochloride
Carbinoxamine Maleate
Bromodiphenhydramine Hcl
Clemastine Fumarate.

(ii) Ethylenediamine
eg. Tripelennamine Citrate
Pyrilamine Maleate,
Methapyrilene Hydrochloride,
Thonzylamine Hydrochloride.

(iii) Propylamine derivatives
eg. Chlorpheniramine Maleate,
Pheniramine Maleate,
Triprolidine HCl,
Bromopheniramine Maleate.
(iv) Phenothiazine derivatives
eg. Promethazine HCl,
Trimeprazine tartrate
Methdilazine HCl.
(v) Piperazine derivatives
eg. Cyclizine HCl,
Chlorcyclizine HCl,
Meclizine HCl,
Buclizine HCl.

(vi) Dibenzocycloheptenes
eg. Cyproheptadiene HCl,
Azatadine Maleate.
(vii) Miscellaneous drugs
eg. Diphenylpyraline HCl,
Dimethindene Malete,
Antazoline Phosphate.

B. Second generation antihistamines

The second-generation antihistamines bind only to peripheral H1 receptors and reduce with little or no sedation.
Eg. Cetrizine
Lortidine Fexofenadine hcl.The H1 antagonists are referred first-generation Or classic antihistamines.


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