A method is disclosed for providing extended duration treatment or prevention of pain, inflammation and inflammation-related disorders in a subject in need of such extended duration treatment or prevention by administering to the subject a Cox-2 selective inhibitor having certain added substituent groups. Also disclosed is a method for extending the duration of the plasma half-life of diaryl-substituted Cox-2 selective inhibitors by substituting halogen, haloalkyl, haloalkoxy, alkyl, nitrile, cyano or alkoxy groups at certain positions on the diaryl-substituted rings of the inhibitor molecule. A novel composition comprising such extended duration Cox-2 selective inhibitors is also disclosed.