The present invention relates to carbapenems and provides a compound of the formula (I) ##STR1## wherein: R.sup.1 is 1-hydroxyethyl, 1-fluoroethyl or hydroxymethyl; R.sup.2 is hydrogen or C.sub.1-4 alkyl; R.sup.3 is hydrogen or C.sub.1-4 alkyl; A is a 5-membered heteroaryl ring containing one nitrogen atom and up to two additional heteroatoms selected from nitrogen, oxygen and sulphur; and is bonded to the nitrogen of the linking carbamoyl group by a carbon atom in the ring, is substituted with the carboxy group on a carbon atom in the ring and is optionally further substituted on a carbon atom in the ring; and in any ring --NH--, H is optionally replaced by C.sub.1-4 alkyl; or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof. Processes for their preparation, intermediates in their preparation, their use as therapeutic agents and pharmaceutical compositions containing them are also described.