The invention thus provides the compounds of formula (I) and pharmaceutically acceptable salts thereof, in which: R1 and R2 are independently selected from the group consisting of H, C1-6alkyl, C2-6alkenyl, C3-6alkynyl, C3-10cycloalkylC0-6alkyl and C4-12bridged cycloalkyl; R3 is selected from the group consisting of C1-6alkyl, NH2 and R5CONH; R4 is selected from the group consisting of CH2F, CHF2, CF3CH2, CF3CHF and CF3CF2; and R5 is selected from the group consisting of H, C1-6alkyl, C1-6alkoxy, C1-6alkylOC1-6alkyl, phenyl, HO2CC1-6alkyl, C1-6alkylOCOC1-6alkyl, C1-6alkylOCO, H2NC1-6alkyl, C1-6alkylOCONHC1-6alkyl and C1-6alkylCONHC1-6alkyl. Compounds of formula (I) are potent and selective inhibitors of COX-2 and are of use in the treatment of the pain, fever, inflammation of a variety of conditions and diseases.