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Zafirlukast is a selective cysteinyl leukotriene receptor antagonist for the treatment of asthma. It acts by binding competitively to cysLT1 receptor against endogenous leukotrienes which cause bronchospasm. Administration should be on an empty stomach because food lowers its oral bioavailability. Elimination is mostly by the liver through CYP2C9 with a half-life of 10 h. The metabolites are excreted through the bile into feces. Zafirlukast relieves leukotrine-induced bronchoconstriction in animals and those induced by allergens, exercise and cold air in humans. Clinical trials show that zafirlukast improves symptoms, peak expiratory flow rate and FEV1 in chronic asthma. These effects are similar to cromolyn sodium but less than those achieved by fluticasone and salmeterol. Bronchoalveolar lavage findings suggest that it has some anti-inflammatory effects. The most common adverse effects are sorethroat, headache and worsening of asthma symptoms. Normal doses do not increase the levels of hepatic transaminases whereas induction of Churg-Strauss syndrome is controversial. Drug interactions occur with co-administration of aspirin, erythromycin, theophylline and warfarin. Zafirlukast is indicated in older children and adults with chronic asthma with inadequate response to inhaled corticosteroids, prevention of exercise-induced asthma and treatment of aspirin induced asthma, but should not be used in acute asthmatic attack.
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