Sulbactam sodium (Axon 2041) is a rather classical, yet weak inhibitor of beta-lactamase (sub-family of cyclic amid hydrolases; EC 3.5.2.6), used to enhance the antibacterial activity of penicillins and cephalosporins against β-lactamase–producing organisms. β-lactamases may be grouped into four classes, of which A, C, and D are serine hydrolases, and B encompasses metallo-β-lactamases. During several decades, not only have the class A and C enzymes become widely disseminated so as to become the most widespread causes of β-lactam antibiotic-resistant Gram-negative infections in Europeand North America, but many mutant forms have also evolved which are capable of hydrolyzing the expanded-spectrum β-lactam antibiotics.