Stable pharmaceutical formulations of montelukast sodium

A stable montelukast pharmaceutical composition comprising montelukast or a salt thereof and at least one pharmaceutically acceptable excipient, wherein the pharmaceutically acceptable excipient is chosen by:

• a) providing a mixture of montelukast and a pharmaceutically acceptable excipient wherein the pharmaceutically acceptable excipient is present in an amount that does not increase the amount of the corresponding sulfoxide of montelukast in the composition to exceed 1% by weight of the initial amount of montelukast after the composition has been stored at about 55° C. for 48 hours;
• b) storing the mixture at 55° C. for 48 hours;
• c) determining the presence and amount of a montelukast sulfoxide in the mixture;
• and
• c) selecting the pharmaceutically acceptable excipient that does not increase the amount of the corresponding sulfoxide of montelukast in the mixture to exceed 1% by weight of the initial amount of montelukast in the mixture.