[Effect of loratadine, selective antagonist of histamine H1 receptors, on histamine-induced bronchoconstriction]

The aim of this study was to assess the duration of Loratadine effect on histamine H1 receptor in the airway. Six patients with mild or moderate asthma were examined. Bronchial reactivity to histamine was measured according to Cockcroft. The significant blockade of histamine H1 receptors in airway was observed from the 2nd day when 10 mg of Lo was given daily. The maximal protection with 10 mg doses was observed after 3-4 days. After another 5-6 days without Loratadine bronchial responsiveness return to the initial values. Single dose of 30 mg Loratadine given better protection against histamine bronchoconstriction than 10 mg given for 5 days. This effect was observed as early as 60 minutes after administration of Loratadine.