The extended-spectrum penicillins can be categorized into two classes: carboxypenicillins and ureidopenicillins. The major antimicrobial agent in the carboxypenicillin class is ticarcillin and in the ureidopenicillin class is piperacillin. These agents have similar spectra of activity as ampicillin. Ampicillin has activity against most streptococci, enterococci, nonbeta-lactamase-producing species of Haemophilus influenzae, and gram- negative enteric pathogens, such as Escherichia coli. Ticarcillin and piperacillin have extended activity against many gram-negative organisms, including Proteus, Enterobacter, and Pseudomonas sp. 

Ticarcillin and piperacillin rarely are indicated in community-acquired infections; they are used frequently in combination with other antimicrobial agents for empiric therapy of nosocomial pneumonia, bacteremia, and urinary tract infections. The gram-positive coverage of these two agents can be improved for methicillin-susceptible Staphylococcus aureus by the addition of a beta-lactamase inhibitor (ticarcillin-clavulanic acid or piperacillin-tazobactam). However, the beta-lactamase inhibitor might not improve the gram-negative coverage, such as for Pseudomonas.

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