Protection against histamine-induced bronchoconstriction by loratadine.

In a simple blind pilot study we have examined the protective effect of loratadine, a new H1 histamine receptor antagonist, against bronchoconstriction induced by histamine inhalation. Six patients with an episodic or continuing obstructive bronchial disease and proven bronchial hyperreactivity were submitted to two identical histamine challenges, first without premedication and then after three days' treatment with 10 mg loratadine daily. The mean FEV1 fall in the first test after histamine inhalation was 33% and in the second test after pretreatment with loratadine only 3.3% (p less than 0.01). Five out of six patients have shown complete protection against histamine-induced bronchoconstriction, in one patient the protection was partial. We conclude that loratadine effectively inhibits histamine-induced bronchoconstriction and could be useful in the prophylactic treatment of asthma and obstructive bronchitis.