 The primary actions of these drugs are that they block the action of leukotrienes, by binding to the receptor with antagonistic action without having an agonistic effect.The primary purpose of the antagonists is to block the actions of leukotriene D4 (LTD4) By competing with LTD4 it will result in reduced effect by the leukotrienes, for example, LTD4 which has bronchoconstriction and vasoconstricting effect, as well as bronchial asthma and inflammation.When comparing the pharmacokinetic properties of montelukast and zafirlukast the two drugs have many similarities.