HSR6071 is an antiallergic agent with potential for the treatment of asthma. In Vivo: HSR-6071 suppresses antigen-induced histamine and SRS-A release from minced lung tissues of guinea-pigs sensitized passively with rabbit anti-EA serum and is a more potent inhibitor of the release of SRS-A than of histamine. On the other hand, histamine- or acetylcholine-induced bronchoconstriction in guinea-pigs is scarcely affected by HSR-6071 at doses sufficient to inhibit the experimental asthma, but LTD4-induced bronchoconstriction is dramatically inhibited. HSR-6071 inhibits cyclic AMP phosphodiesterase activity and produces relaxation of the guinea-pig isolated trachea^[1]. HSR-6071 inhibits the IgE-mediated histamine release with an IC₅₀ of 0.46 nM. HSR-6071 is effective not only by i.v. but also by p.o. administration on the IgE mediated PCA in rats. The most potent inhibition with HSR-6071 is observed when it is given p.o. 5 min before the antigen challenge, indicating the rapid absorption of HSR-6071 through the gastrointestinal tract^[2].