IMMUNOLOGY

Detailed explanation-1: -Antihistamine (H1 blocker) of the piperazine class. Like other antihistamines, hydroxyzine acts by blocking the H1 receptor and suppresses inflammatory reactions caused by histamine. The H1 blockers have been used to control pruritus and skin inflammation, rhinorrhea, and airway inflammation.

Detailed explanation-2: -Antihistamines bind to either H1 or H2 histamine receptors, thereby blocking histamine’s effects in the body. These medications act as inverse agonists, rather than receptor antagonists, by downregulating the activated state of histamine receptors.

Detailed explanation-3: -Histamine Receptors Classical H1-receptor antagonists, including mepyramine, chlorpheniramine, promethazine, diphenhydramine, and cyproheptadine, are used as systemic and/or topical preparations in the management of allergic reactions (i.e., hay fever, allergic rhinitis, insect bites, and anaphylactic reactions).

Detailed explanation-4: -The second generation H1-antihistamines do not cross the blood brain barrier which is why it does not cause drowsiness such as the first generation. The H2-antihistamines block H2 histamine receptors that are found in the gastric acid producing parietal cells of the stomach.