Comparative in vitro activity and beta-lactamase stability of moxalactam and other selected cephalosporin antibiotics.

(6R, 7R)-7-[[Carboxy(4-hydroxyphenyl)-acetyl]amino]-7-methoxy-3[[(1-methyl-1H-tetrazol-5-yl)thio]methyl]-8-oxo-5-oxa-1-azabicyclo[4,2,0]oct-2-ene-2-carboxylic acid (moxalactam, LY 127 935), a novel 1-oxa-beta-lactam, was proved to display similar antibacterial activity as cefotaxime against a number of beta-lactamase-producing gram-negative strains. The outstanding activity proved to be bactericidal in most cases and was only slightly influenced by variation of the inoculum size. The activity of cefotaxime and especially cefamandole on the contrary had rather a high inoculum-dependence. Moxalactam had equal stability to gram-negative beta-lactamases as has cefoxitin. Like cefotaxime and cefoxitin, the compound proved to be a potent inhibitor of cephalosporinases but not of broad spectrum beta-lactamases.