Mahaveer Kabra*1, Sanjay Bhandari1, Ami Sharma1, Reema Jain2
Department of Pharmacology,
1Kota College of Pharmacy, Kota
2Bhupal Noble’s Institute of Pharmaceutical science, Udaipur
A histamine antagonist is an agent which serves to inhibit the release or action of histamine. Allergies are caused by an excessive response of the body to allergens, such as the pollen released by grasses and trees. An allergic reaction indicates an excessive release, of histamine by the body.Histamine is a natural chemical produced by the immune (disease-fighting) system of the body. The main action of histamine is related to allergies. An allergen is a substance that is not normally harmful, such as pollen, but which causes an overreaction by the immune system in some people.drugs show their action by binding with their specific receptor like H1-receptor antagonists are Diphenhydramine, Meclizine etc. H2-receptor antagonists Cimetidine, Famotidine. All antihistamines are reversible, competitive antagonists at histaminic (H1) receptors. They act by inhibiting binding of circulating histamine to its receptor site, but do not prevent histamine release. Administration of an antihistamine results in inhibition of respiratory, vascular, and gastrointestinal smooth muscle constriction, a decrease in histamine-activated secretions from salivary and lacrimal glands, and anti-inflammatory effects. Antihistamines also decrease capillary permeability, which reduces the wheal and flare response to an allergen, as well as diminishes itching. Competitive inhibition of histamine at H2 receptors of the gastric parietal cells resulting in reduced gastric acid secretion, gastric volume and hydrogen ion concentration reduced. Antihistamines are used as treatment for allergies.