| Pharmacodynamics |
In allergic reactions an allergen interacts with and cross-links
surface IgE antibodies on mast cells and basophils. Once the mast
cell-antibody-antigen complex is formed, a complex series of events
occurs that eventually leads to cell-degranulation and the release of
histamine (and other chemical mediators) from the mast cell or basophil.
Once released, histamine can react with local or widespread tissues
through histamine receptors. Histamine, acting on H1-receptors,
produces pruritis, vasodilatation, hypotension, flushing, headache,
tachycardia, and bronchoconstriction. Histamine also increases vascular
permeability and potentiates pain. Mequitazine is a histamine H1
antagonist. It competes with histamine for the normal H1-receptor
sites on effector cells of the gastrointestinal tract, blood vessels
and respiratory tract. It provides effective, temporary relief of
sneezing, watery and itchy eyes, and runny nose due to hay fever and
other upper respiratory allergies. |
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