CEPHALOSPORINANTIBIOTIKA

Cephalosporin antibiotics of general formula (I) (wherein R1 and Rb, which may be the same or different, each represent a C1-2 alkyl group, or together with the carbon atom to which they are attached form a C3-6 cycloalkylidene group and Y(+) represents a 1-carbamoylmethylpyridinium group) exhibit broad spectrum antibiotic activity, the activity being unusually high against gram-negative organisms such as strains of Pseudomonas organisms. Particularly effective compounds of formula (I) are (6R,7R)-7-[(Z)-2-(2-aminothiazol-4-yl)-2-(2-carboxyprop-2-oxyimino)ace tamido]-3-[(1-carbamoylmethylpyridinium-4-yl)thiomethyl]ceph-3-em-4-ca rboxylate and (6R,7R)-[(Z)-2-(2-aminothiazol-4-yl)-2-[(1-carboxycyclobut-1-oxyimino) acetamido]-3-[(1-carbamoylmethylpyridinium-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), compositions containing the antibiotic compounds of the invention and processes for the preparation of the antibiotics.