Cetirizine inhibition of histamine-induced bronchospasm

Cetirizine is a potent, selective H1 antagonist recently made available for investigation. To evaluate this oral drug's efficacy in treating asthma, we examined the bronchodilator effects of 5-, 10-, and 20-mg doses as well as the protective effects of these doses against histamine-provoked bronchospasm. Cetirizine's efficacy was compared with that of a placebo and oral hydroxyzine (25 mg) in 10 patients with mild asthma. The new compound provided significant protection in a dose-dependent manner against histamine-induced bronchospasm. A 25-mg oral dose of hydroxyzine, which is partially metabolized to cetirizine, yielded blood levels of cetirizine comparable to those attained with 5 mg of oral cetirizine. Hydroxyzine 25 mg conferred greater protection against histamine bronchoprovocation than placebo, but it gave less protection than 10- and 20-mg doses of cetirizine. Cetirizine in all doses, as well as hydroxyzine at 25 mg, produced significant bronchodilation. However, the bronchodilator effect of the 25-mg hydroxyzine dose was less than that of cetirizine at 20 mg. In this short-term study, no significant side effects of cetirizine were noted.