NCIt definition : The hydrochloride salt form of meclizine, a synthetic piperazine with anti-emetic,
sedative and histamine H1 antagonistic properties. Meclizine hydrochloride blocks
the H1 histamine receptor and prevents the symptoms that are caused by histamine activity
on capillaries, bronchial and gastrointestinal smooth muscles, including vasodilation,
increased capillary permeability, bronchoconstriction, and spasmodic contraction of
gastrointestinal smooth muscles. Meclizine hydrochloride may exert its antiemetic
effects by its anticholinergic actions or due to a direct effect on the medullary
chemoreceptive trigger zone.;