Pirodomast is Thromboxane A (TXA2) synthetase inhibitor. Pirodomast can inhibit leukotriene (LT) D4, C4, E4 formation and Thromboxane B2 (TXB2) activities. It was weak or ineffective as an antagonist of histamine, methacholine, serotonin, LTC4 or platelet activating factor induced bronchospasms in guinea pigs. Also, pirodomast was not a bronchodilator or calcium influx blocker and had only weak relaxant activity on guinea pig trachea in vitro. Pirodomast is, therefore, a potential antiallergic agent that inhibits leukotriene (LT) release. Pirodomast inhibited tryptase proteolytic activity in-vitro. In experimental studies in vivo, pirodomast blocked antigen-induced immediate and late asthmatic responses in allergic sheep. Pirodomast inhibited antigen-induced airway hyperresponsiveness to both histamine and carbachol in allergic sheep. Pirodomast was being investigated for use in asthma and allergic rhinitis.