Suppression of the histamine-induced wheal and flare response by fexofenadine HCl 60 mg twice daily, loratadine 10 mg once daily and placebo in healthy Japanese volunteers

Summary

Background: The effects of the selective H₁-receptor antagonist fexofenadine have been widely demonstrated in Western populations; however, to date, limited data comparing the effects of fexofenadine with other antihistamines have been reported in Japanese subjects.

Objective: To investigate the effect of fexofenadine and loratadine on the histamine-induced cutaneous wheal and flare response in healthy Japanese volunteers.

Methods: Eighteen healthy male and female Japanese volunteers aged 20-53 years were randomized to receive fexofenadine HCl 60 mg twice daily, loratadine 10 mg once daily or placebo in a 1-day, three-period, double-blind, crossover study. For each treatment, the wheal and flare response to 100 mg/mL histamine was assessed at baseline and at 1, 1.5, 2, 2.5, 3, 3.5, 4, 8, 12 and 24 hours post-dose. Blood samples were taken for pharmacokinetic analysis.

Results: Fexofenadine produced significantly greater percentage suppression of the overall wheal response compared with placebo and loratadine (43.1% versus 10.0% and 15.2%, respectively; p < 0.001). Similarly, fexofenadine significantly suppressed the overall flare response compared with placebo and loratadine (43.0% versus 3.5% and -8.9%, respectively; p < 0.01). Loratadine was statistically no different from placebo in terms of both overall wheal and flare suppression. Area under the curve analysis for wheal and flare reduction (0-12 hours post-dose) confirmed these findings. For wheal inhibition, fexofenadine had a significantly faster onset of action (defined as time to ≥ 35% inhibition) compared with placebo (p < 0.001) and loratadine (p < 0.01); for flare, fexofenadine had a significantly faster onset of action than loratadine (p < 0.01). Mean maximum inhibition (the mean of the greatest inhibition achieved from baseline for each treatment) for wheal was achieved significantly faster with fexofenadine than loratadine (p < 0.01), and fexofenadine had a significantly longer duration of effect on suppressing wheal and flare compared with placebo and loratadine (p < 0.05 for all). The antihistamine effects of fexofenadine correlated significantly with its C_max, while loratadine activity did not correlate significantly with its plasma levels.

Conclusions: Fexofenadine is a potent suppressor of the histamine-induced wheal and flare response in healthy Japanese volunteers. These results support findings in Caucasian subjects, and confirm that fexofenadine has greater antihistaminergic activity than loratadine in this human model

Key Words::

• Antihistamines
• Fexofenadine
• Japanese
• Loratadine
• Wheal and flare