Cefotaxime(1-) is a cephalosporin carboxylic acid anion having acetoxymethyl and [2-(2-amino-1,3-thiazol-4-yl)-2-(methoxyimino)acetyl]amino side-groups, formed by proton loss from the carboxy group of the cephalosporin cefotaxime. It is a conjugate base of a cefotaxime.