Cephalosporin antibiotics

Abstract

Cephalosporin antibiotics of general formula: ##STR1## (wherein R.sup.a and R.sup.b, which may be the same or different, each represent a C.sub.1-4 alkyl group or R.sup.a and R.sup.b together with the carbon atom to which they are attached form a C.sub.3-7 cycloalkylidene group, and Y.sup..sym. represents a C-linked 5- or 6-membered heterocyclic ring containing at least one C.sub.1-4 alkyl-substituted quaternary nitrogen atom, which ring may also contain one or more sulphur atoms) exhibit broad spectrum antibiotic activity, the activity being unusually high against gram-negative organisms such as strains of Pseudomonas organisms. A particular antibiotic compound of formula (I) possessing excellent antibacterial activity against strains of Pseudomonas organisms, as well as other valuable therapeutic properties, is (6R,7R)-7-[(Z)-2-(2-aminothiazol-4-yl)-2-(1-carboxycyclobut-1-oxyimino)ace tamido]-3-[(1-methylpyridinium-4-yl)-thiomethyl]ceph-3-em-4-carboxylate. The invention also includes the non-toxic salts and non-toxic metabolically labile esters of compounds of formula (I). Also described are compositions containing the antibiotics of the invention and processes for the preparation of the antibiotics.