Zafirlukast

Zafirlukast is in a class of medications called leukotriene receptor antagonists (LTRAs). It works by blocking the action of certain natural substances that cause swelling and tightening of the airways. In a study, pranlukast or zafirlukast significantly inhibited 10 μM LTD4-evoked 35SO4 output in a concentration- dependent fashion, with maximal inhibitions of 83% at 10 μM pranlukast and 78% at 10 μM zafirlukast, and IC50 values of 0.3 μM for pranlukast and 0.6 μM for zafirlukast. Both pranlukast and zafirlukast showed moderate inhibition of CYP2C9-catalysed tolbutamide 4-methylhydroxylation, competitively inhibiting tolbutamide 4-methylhydroxylation with estimated mean Ki values of 3.82 ± 0.50 and 5.86 ± 0.08 μM, respectively.Zafirlukast inhibited the hydroxylation of tolbutamide (CYP2C9; mean IC50=7.0 µM).