Antagonists that selectively block specific histamine receptors have been developed. H1 antagonists block the actions of histamine responsible for increased capillary permeability and wheal and edema formation. H1 antihistamines may be useful in the treatment of the immediate hypersensitivity reactions such as anaphylaxis by blocking bronchoconstriction and vasodilation. H1 antagonists may be less effective in the treatment of inflammatory diseases and allergic reactions such as atopy, primarily because mediators other than histamine play important roles in such conditions. H2 (now classified as inverse agonists of the H2 receptor, such as cimetidine and ranitidine) antagonists are routinely used to block the gastric secretory effects of histamine and have limited anti-inflammatory effects.
Last full review/revision March 2012 by Pierre-Louis Toutain, DVM, PhD, DECVPT