| abstract |
A cephalosporin derivative of the formula I: ##STR1## in which X is S, O, CH 2 or SO, R1 is (optionally-substituted)imidazol-2-yl or one of the C-7 acyl groups known in the cephalosporin art, R2 is hydrogen or methoxy, R3 is carboxy or a biodegradable ester thereof and --R4 is of the formula XII, XIII or XIV: ##STR2## in which R32-R40 inclusive are as defined in the specification; and the salts thereof. Pharmaceutical compositions, methods of manufacture and intermediates are also described. |