A SULFONE ;3-LACTAM COMPOUND WHICH ACTS AS A i3-LACTAMASE INHIBITOR

CP-45,899 [3,3-dimethyl-7-oxo-4-thia-l-azabicyclo(3,2,0)heptane-2-carboxylic acid, 4,4dioxide, [2S-(2a,5a)]] has low intrinsic activity against most Gram-positive cocci, Enterobacteriaceae and Pseudomona . It inhibits Neisseria at concentrations of 0.1 -6.2 lig/ml. The combination of CP-45,899 and ampicillin inhibited Staphylococcus aureus and En tero bacteriaceae resistant to ampicillin by virtue of (3-lactamase activity. Combination of CP-45,899 and cephalothin was synergistic less often, and CP-45,899 did not act synergistically with carbenicillin or ticarcillin against Pseudoinonas resistant to these agents. CP-45,899 acted synergistically with ampicillin against Bacteroides. Synergy of CP-45,899 and ampicillin was demonstrated at varying concentrations suggesting that it may significantly enlarge the antibacterial activity of ampicillin against resistant bacteria.