Penicillins, monobactams, carbapenems, imipenems, and cephalosporins are known chemically as beta-lactam antibiotics because as part of their chemical structure they contain what is know as a beta-lactam ring. The above illustration shows the basic structure of penicillin, cephalosporin, imipenem, and clavulanate. "R" represents sites where different chemical side chains attach, depending on the particular antibiotic.

Some bacteria produce various beta-lactamases, enzymes that break the beta-lactam ring at the site indicated by the arrows, and are able to inactivate some forms of these drugs.

Clavulanate and sulbactam are drugs that resemble beta-lactam antibiotics. These agents are sometimes added to beta-lactam antibiotics to tie up and, therefore, inactivate the bacterial beta-lactamases.