The antiallergic effects of antihistamines (H1-receptor antagonists).

Most first-generation and second-generation H1-receptor antagonists have readily demonstrable antiallergic effects in vitro, although high concentrations of some of the medications are required to inhibit mediator secretion from mast cells or basophils. These antiallergic effects can also be seen in vivo in skin, nasal, lung, and ocular challenge studies. Some H1-receptor antagonists appear to have an antiallergic effect in one organ but not in another. In many in vivo studies, doses of H1-receptor antagonists three or more times higher than those required for H1 blockade must be given to achieve the antiallergic effect. It would be premature to attempt to reclassify the H1 antagonists according to their antiallergic properties because these properties have not been investigated fully and their relative contribution to the overall therapeutic effectiveness of each H1 receptor antagonist is unknown.