Duration of effect of loratadine and terfenadine administered once a day for one week on cutaneous and inhaled reactivity to histamine.

STUDY OBJECTIVE The duration of action of several new non-sedative antihistamine preparations as assessed by skin and bronchial reactivity to histamine has still not been well established. The aim of the study was to evaluate the duration of effect of loratadine (10 mg) and terfenadine (120 mg) administered once a day for one week on cutaneous and inhaled reactivity to histamine by comparison with a placebo. SUBJECTS Twenty-four adult asthmatic subjects were included in a parallel group study that compared the duration of effect of two antihistamines and a placebo on cutaneous and inhaled reactivity to histamine. STUDY DESIGN Baseline cutaneous and inhaled reactivity (concentration causing a fall of 20 percent in FEV1 [PC20]) to histamine was obtained on three consecutive days. Loratadine (10 mg), terfenadine (120 mg) and a placebo loratadine were administered daily for 1 week to 3 groups of subjects. The PC20 was measured at the end of the medication period, 3 days later, and weekly until PC20 returned to baseline value (upper limit of 2 SD from the mean baseline value). RESULTS The mean blocking duration on cutaneous reactivity for loratadine was 6.9 days and for terfenadine, 7.2 days. The mean duration of the blocking effect on PC20 histamine was 8.5 days for loratadine and 7.2 days for terfenadine. These figures were significantly longer than for the placebo. CONCLUSION These data suggest that terfenadine and loratadine have a comparable blocking effect on reactivity to cutaneous and inhaled histamine. A daily dose taken for one week will result in a mean blocking effect of one week.