Sedating antihistamines mechanism of action
By inhibiting the activity of histamine, they can reduce capillary fragility, which produces the erythema, or redness, associated with allergic reactions.They will also reduce histamineinduced secretions, including excessive tears and salivation.Additional effects vary with the individual drug used.
The second generation antihistamines have no central action, and are used only for treatment of allergic reactions. Cetirizine (Zyrtec) is a piperazine derivative, and has a slight sedative effect.
Loratidine (Claritin) and fexofenadine (Allegra) are members of the piperadine class and are essentially non-sedating.
When used for control of allergic reactions, antihistamines should be taken on a regular schedule, rather than on an as-needed basis, since they have no effect on histamine itself, nor on histamine already bound to the receptor site.
receptor sites, responsible for immediate hypersensitivity reactions such as sneezing and itching.
Members of this class of drugs may also be used for their side effects, including sedation and antiemesis (prevention of nausea and vomiting). They have no effect on rate of histamine release, nor do they inactivate histamine.