<unk>  is a broad-spectrum β-lactam antibiotic of the ureidopenicillin class. The chemical structure of<unk>  and other ureidopenicillins incorporates a polar side chain that enhances penetration into Gram-negative bacteria and reduces susceptibility to cleavage by Gram-negative beta lactamase enzymes. These properties confer activity against the important hospital pathogen Pseudomonas aeruginosa. Thus<unk>  is sometimes referred to as an "anti-pseudomonal penicillin". When used alone,<unk>  lacks strong activity against the Gram-positive pathogens such as Staphylococcus aureus, as the beta-lactam ring is hydrolyzed by the bacteria's beta-lactamase. It was patented in 1974 and approved for medical use in 1981.<unk>  is most commonly used in combination with the beta-lactamase inhibitor tazobactam<unk> /tazobactam), which enhances<unk> 's effectiveness by inhibiting many beta lactamases to which it is susceptible. However, the co-administration of tazobactam does not confer activity against MRSA, as penicillin (and most other beta lactams) do not avidly bind to the penicillin-binding proteins of this pathogen. The World Health Organization classifies<unk>  as critically important for human medicine.
Piperacillin
Cloxacillin
Resistin
Carbenicillin
Cefazolin
Ampicillin
Dicloxacillin
Vancomycin