A new cephalosporin with a dual mode of action.

A cephalosporin, (6R,7R)-7-[(2R)-2-hydroxy-2-phenylacetamido]-3-(pyrid-2-yl-N-oxide) thiomethylceph-3-em-4-carboxylic acid (MCO), that could lead to a novel approach to the problem of beta-lactamase destruction is described. The compound is slightly more resistant to some beta-lactamases than is cephalothin, but it is still hydrolyzed by many to a varying degree. Hydrolysis of the beta-lactam bond of a cephalosporin releases the 3-substituent, which in MCO is itself an antibacterial agent, 2-mercaptopyridine-N-oxide. Thus, MCO has a dual mode of action, and bacteria that do not produce an effective amount of a beta-lactamase are inhibited by the intact cephalosporin, whereas those that do hydrolyze it are inhibited by the released antibacterial compound.