7{62 -{8 2-Etherified oximino-2-(phenyl- or naphthylacetamido){9 {0 cephalosporins

The invention provides novel antibiotic compounds which are 7 beta -acylamidoceph-3-em-4-carboxylic acids, and non-toxic derivatives thereof characterized in that the acylamido group has the structure where R is a hydrogen atom or an organic group and Ra is an etherifying monovalent organic group linked to the oxygen atom through a carbon atom. The compounds are syn isomers or exist as mixtures containing at least 75% of the syn isomer. These antibiotic compounds possess high antibacterial activity against a range of gram positive and gram negative organisms coupled with particularly high stability to beta -lactamases produced by various gram negative organisms. The invention is also concerned with the administration of the compounds.