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