Sulbactam: Biochemical Factors Involved in Its Synergy with Ampicillin

Sulbactam is a time-dependent irreversible inhibitor of various β-lactamases by reversible formation of a Michaelis-type enzyme-inhibitor complex and progressive evolution of this complex into inactivated protein(s). This process is either irreversible (true inactivation) or quasi-irreversible (stable acyl-enzyme). In this way, sulbactam efficiently protects ampicillin from degradation by β-lactamases. Sulbactam itself exhibits a moderate antibacterial activity that is related to an affinity for the penicillin-binding proteins of various bacterial strains, which is similar to the affinity of penicillins such as ampicillin. However, sulbactam binding differs according to the bacterial species involved. In strains producing either low levels of β-lactamase or none at all, a synergistic effect, minor but not negligible, can be observed when sulbactam is associated with a β-lactam antibiotic with a complementary affinity for the target sites.