An oxacephem is a β-lactam molecule similar to a

cephem Cephems are a sub-group of β-lactam antibiotics including cephalosporins and cephamycin Cephamycins are a group of β-lactam antibiotics. They are very similar to cephalosporins, and the cephamycins are sometimes classified as cephalosporins. ...

, but with an oxygen substituted for the sulfur. They are synthetic compounds not seen in nature, generally used as

β-lactam antibiotic β-lactam antibiotics (beta-lactam antibiotics) are antibiotics that contain a beta-lactam ring in their chemical structure. This includes penicillin derivatives (penams), cephalosporins and cephamycins (cephems), monobactams, carbapenems and ...

s. Examples include Latamoxef and Flomoxef.

References

Antibiotics {{antibiotic-stub