Disclosed are the compounds of formula I wherein R is methyl or ethyl; R1 is chloro or fluoro; R2 is hydrogen or fluoro; R3 is hydrogen, fluoro, chloro, methyl, ethyl, methoxy, ethoxy or hydroxy; R4 is hydrogen or fluoro; and R5 is chloro, fluoro, trifluoromethyl or methyl; and pharmaceutically acceptable salts thereof, as selective COX-2 cyclooxygenase inhibitors; and pharmaceutically acceptable prodrug esters thereof.