[Effect of loratadine (LO), a selective H1 antagonist, on histamine-induced bronchoconstriction]

The influence of single and repeated LO (10 mg/day) doses on histamine-induced bronchoconstriction was studied in 11 patients with stabile bronchial asthma. Bronchial reactivity was estimated as histamine content potent to elicit a 20% FEV, fall, i.e. PC20H. A single dose gave a significant (5.5 fold) reduction in bronchial reactivity to inhaled histamine. Application of LO during 6 days gave a similar effect. Withdrawal of LO for 6 days yielded an increase in bronchial hyperreactivity.