Inhibitory activity of terfenadine on histamine-induced skin wheals in man

The inhibitory effect of orally administered terfenadine on the area of histamine-induced skin wheals was studied by single dose and multiple dose trials in 12 normal male volunteers. Single doses of 20, 60 and 200 mg of terfenadine produced dose-dependent decreases in histamine wheal area that reached a maximum by the fourth hour after dosing. The 60 and 200 mg doses blocked almost 90% of histamine whealing, and significant reduction of the wheal area persisted for 8 h. During the multiple dose trial histamine whealing was markedly inhibited after the fifth and sixth dose of terfenadine 20, 40 or 60 mg every 8 h and of 60 mg every 12 h. On the last three dosage schedules inhibition persisted for at least 12 h after the final dose. Inhibition of histamine-induced skin whealing appears to be a quantitative index of the time course of histamine H1-receptor antagonist action.