Abstract
The interactions of E1040 with cephalosporinase from Citrobacter freundii, including affinity and hydrolysis, were studied in comparison with those of cefotaxime and ceftazidime. E1040 showed a higher stability at low drug concentrations and a much lower affinity for the enzyme than did cefotaxime or ceftazidime. These enzymological properties explain the high activity of E1040 against cephalosporinase-producing C. freundii.