antibioticsbooks

66 PART 2 Antibacterial Drugs
enhance the activity. Therefore, the combination
products are active only against the bacteria that
the beta-lactam in the combination has intrinsic
activity against. For example, ampicillin/sulbactam
is active against beta-lactamase producing E. coli,
because ampicillin alone is active against non- betalactamase
producing E. coli. However, it has no
useful activity against Pseudomonas aeruginosa,
because ampicillin lacks activity against this organism.
In contrast, piperacillin/tazobactam is active
against P. aeruginosa because piperacillin alone is
useful. Though these drugs have very broad spectra
of activity, there are differences among the agents.
Keep in mind the rule that beta-lactamase inhibitors
restore activity, not add to it, to set them straight.
Mechanism of Action
All beta-lactams inhibit cross-linking of peptidoglycan
in the cell wall, leading to autolysis and
cell death. Beta-lactamase inhibitors structurally
resemble beta-lactams and bind to many betalactamases,
rendering them unable to inactivate
the co-administered beta-lactam.
Spectrum
Good: MSSA, streptococci, enterococci, many anaerobes,
enteric GNRs, Pseudomonas aeruginosa
(only piperacillin/ tazobactam and ticarcillin/
clavulanate)
Moderate: GNRs with advanced beta-lactamases
Poor: MRSA, extended-spectrum beta-lactamase
(ESBL) producing GNRs
Adverse Effects
Similar to those of other beta-lactams.