cephamycin cephamycin cephamycins are a group of β-lactam antibiotics. they are very similar to cephalosporins, and the cephamycins are sometimes classified as cephalosporins. core structure of the cephamycins. like cephalosporins, cephamycins are based upon the cephem nucleus. unlike most cephalosporins, cephamycins are a very efficient antibiotic against anaerobic microbes. cephamycins were originally produced by streptomyces, but synthetic ones have been produced as well. cephamycins possess a methoxy group at the 7-alpha position. in addition, cephamycins have been shown to be stable against extended-spectrum beta-lactamase (esbl) producing organisms, although their use in clinical practice is lacking for this indication. examples cephamycins include: cefoxitin cefotetan cefmetazole