Inhibition of skin reactivity by antihistamines.

A number of studies have explored the inhibition of antigen-induced skin hypersensitivity reactions by the newer, nonsedating antihistamines such as terfenadine. The collective results of these studies indicate that this inhibitory effect begins within two hours of the administration of a single dose of terfenadine and within three to four days of a single dose of astemizole. Offset of this effect occurs within forty-eight hours of cessation of terfenadine therapy and four weeks or more after the withdrawal of astemizole. The time of onset and offset of this inhibitory effect is indicative of the period of clinical activity of these drugs and thus may be a relevant consideration in selecting an appropriate therapeutic regimen.