THE EFFECT OF ANTIHISTAMINES ON THE IMMEDIATE ALLERGIC RESPONSE - A COMPARATIVE REVIEW

Antihistamines are believed to reduce the sneezing and rhinorrhea asso ciated with allergic rhinitis, primarily by competitive antagonism of histamine for H-1 cellular receptors, but additional mechanisms of act ion may contribute to their clinical efficacy. To improve our understa nding of H-1 antihistamine action, we studied the effects of pretreatm ent with terfenadine, cetirizine, ketotifen, azatadine, diphenhydramin e, and azelastine on increases in vascular permeability, mast cell act ivation, and sneezing induced by nasal challenge with antigen. All stu died antihistamines reduced sneezing, indicating that they all effecti vely antagonize histamine after its release. In addition, terfenadine and topically administered azatadine blocked the release of histamine. Studies with cetirizine and azelastine revealed that these antihistam ines significantly reduced sulfidopeptide leukotriene levels. Terfenad ine and azelastine also reduced kinin production. These results confir m that antihistamines are effective in reducing sneezing and, in some cases, vascular permeability. The findings of these studies also illus trate that the various antihistamines have multiple and different mech anisms of action that may hove implications for their clinical uses.