4-(3-methyl-4-phenylisoxazol-5-yl)benzenesulfonamide Parecoxib Sodium Impurity 39 Parecoxib Sodium Impurity 47 Parecoxib Sodium-28 Parecoxib impurity 33/4-(3-methyl-4-phenylisoxazol-5-yl)benzenesulfonamide 4-(3-Methyl-5-phenylisoxazol-4-yl)benzenesulfonamide Benzenesulfonamide, 4-(3-methyl-5-phenyl-4-isoxazolyl)- Parecoxib Sodium Impurity 78