The present invention relates to carbapenems and provides a compound of the formula (I): or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof wherein: R1 is 1-hydroxyethyl, 1-fluoroethyl or hydroxymethyl; R2 is hydrogen or C1-4alkyl; R3 is hydrogen or C1-4alkyl; R4 and R5 are the same or different and are selected from hydrogen, halo, cyano, C1-4alkyl, nitro, hydroxy, carboxy, C1-4alkoxy, C1-4alkoxycarbonyl, aminosulphonyl, C1-4alkylaminosulphonyl, di-C1-4-alkylaminosulphonyl, carbamoyl, C1-4alkylcarbamoyl, di-C1-4 alkylcarbamoyl, trifluoromethyl, sulphonic acid, amino, C1-4alkylamino, di-C1-4alkylamino, C1-4alkanoylamino, C1-4alkanoyl(N—C1-4alkyl)amino, C1-4alkanesulphonamido and C1-4alkylS(O)n— wherein n is zero; one or two: with the proviso that there is no hydroxy or carboxy substituent in a position ortho to the link to —NR3—. Processes for their preparation, intermediates in their preparation, their use as therapeutic agents and pharmaceutical compositions containing them.