<unk>  is insensitive to beta-lactamase (also known as penicillinase) enzymes secreted by many penicillin-resistant bacteria. The presence of the isoxazolyl group on the side chain of the penicillin nucleus facilitates the β-lactamase resistance, since they are relatively intolerant of side chain steric hindrance. Thus, it is able to bind to penicillin-binding proteins and inhibit peptidoglycan crosslinking, but is not bound by or inactivated by β-lactamases.
Flucloxacillin
Piperacillin
Cloxacillin
Dicloxacillin
Resistin
Vancomycin
Cefazolin
Spiramycin