cefazolin cephalosporin carboxylic acid anion cefazolin(1-) (6R,7R)-3-{[(5-methyl-1,3,4-thiadiazol-2-yl)sulfanyl]methyl}-8-oxo-7-[(1H-tetrazol-1-ylacetyl)amino]-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate chebi_ontology CHEBI:53657 A cephalosporin carboxylic acid anion having [(5-methyl-1,3,4-thiadiazol-2-yl)sulfanyl]methyl and (1<em>H</em>-tetrazol-1-ylacetyl)amino side-groups, formed by proton loss from the carboxy group of cefazolin.