The antihistamines appear to block peripheral stimulation
of the emetic center. They are therefore most ef-fective in motion sickness and inner ear dysfunction,
as is seen in Ménière’s syndrome, labyrinthitis, and
streptomycin ototoxicity. Dimenhydrinate, diphenhydramine,
and meclizine hydrochloride are the three antihistamines
primarily used in the prevention of nausea
from inner ear stimulation.
Several H1 histamine antagonists (e.g., diphenhydramine,
promethazine, and hydroxyzine) have been used
as sedative–hypnotics, since they produce some degree
of sedation.While this sedation is usually considered a
side effect of their antihistaminic activity, in some cases
the sedation is sufficient to allow the drugs to be used
in the treatment of anxiety and sleep disturbances.
For these drugs, the anxiolytic properties are thought
to be a direct consequence of their ability to produce sedation.
Hydroxyzine hydrochloride (Atarax, Vistaril) is the
antihistamine with the greatest use in the treatment of
anxiety. It is often used to reduce the anxiety that is associated
with anesthesia and surgery. It also produces
sedation, dries mucous membranes (via an anticholinergic
mechanism), and has antiemetic activity.
