The physilogical action of
antihistamine is a group of reducing drugs that prevent by
competing at the places in the body where it normally acts. True
antihistamine drugs are competitive inhibitors histamine action and have no visible cut action in an absence. These drugs perform differently to drugs such asepinephrine that are able to play a part as antidotes to histamine by making opposite actions that are physiological. Medicinally use of this
synthetic drug is based upon the evidence that histamine causes many symptoms that cause various allergic disorders. Actually normal histamine is present in tissues in a bound in physiological form that is in active. Only under certain conditions when it is released from the bound form that it exhibits toxicity. Therefore in various allergic conditions these symptoms are relieved by the synthetic drug that are really due to histamine that has been exited from it''s bound form in the tissues. The first synthetic drug to be used therapeutically was antigen, and was introduced in 1942 in france. Later came a similar compound with lower toxicity, named nero-antigen and was developed in the same country. 1945 phenhydramine an ethanol amine derivative was introduced in the united states and there after numerous synthetic drugs were then developed all with the same basic structure. All in all it is one in a group of antihistamine drugs used in the treatment of allergic reactions as hay fever.