ZAFIRLUKAST IS A SELECTIVE AND COMPETITIVE RECEPTOR ANTAGONIST OF LEUKOTRIENE D 4 AND E 4 (LTD 4 AND LTE 4 ), COMPONENTS OF SLOW-REACTING SUBSTANCE OF ANAPHYLAXIS (SRSA). CYSTEINYL LEUKOTRIENE PRODUCTION AND RECEPTOR OCCUPATION HAVE BEEN CORRELATED WITH THE PATHOPHYSIOLOGY OF ASTHMA, INCLUDING AIRWAY EDEMA, SMOOTH MUSCLE CONSTRICTION, AND ALTERED CELLULAR ACTIVITY ASSOCIATED WITH THE INFLAMMATORY PROCESS, WHICH CONTRIBUTE TO THE SIGNS AND SYMPTOMS OF ASTHMA.