The drugs which directly block the histamine receptors which are responsible for the allergies, hay fever, conjunctivitis.
Histamine- meaning ‘tissue amine’ ( histosis- tissue) present in animal tissues or in certain plants. Histamine is present in the granules of the mast cell. Tissues rich in histamine are skin, gastric and intestinal mucosa, lungs, liver and placenta. Non mast cell histamine occurs in the brain, epidermis. Turnover mast cell histamine is slow while that of non mast cell histamine is fast. Histamine is also present in the blood, most body secretions and pathological fluids.