Pharmacotherapeutic group: Antibacterials for systemic use, Combinations of penicillins, including beta-lactamase inhibitors.
ATC code: J01C R05
Mechanism of action
Piperacillin, a broad spectrum, semisynthetic penicillin exerts bactericidal activity by inhibition of both septum and cell wall synthesis.
Tazobactam, a beta-lactam structurally related to penicillins, is an inhibitor of many beta-lactamases, which commonly cause resistance to penicillins and cephalosporins but it does not inhibit AmpC enzymes or metallo beta-lactamases..
Tazobactum extends the antibiotic spectrum of piperacillin to include many beta-lactamase-producing bacteria that have acquired resistance to piperacillin alone.
Phamacokinetic / Pharmacodynamic relationship
The time above the minimum inhibitory concentration (T>MIC) is considered to be the major pharmacodynamic determinant of efficacy for piperacillin.
Mechanism of resistance
The two main mechanisms of resistance to Piperacillin/Tazobactam are:
• Inactivation of the piperacillin component by those beta-lactamases that are not inhibited by tazobactam: beta-lactamases in the Molecular class B, C and D. In addition, tazobactam does not provide protection against extended-spectrum beta-lactamases (ESBLs) in the Molecular class A and D enzyme groups.
• Alteration of penicillin-binding proteins (PBPs), which results in the reduction of the affinity of piperacillin for the molecular target in bacteria.
Additionally, alterations in bacterial membrane permeability, as well as expression of multi-drug efflux pumps, may cause or contribute to bacterial resistance to piperacillin / tazobactam, especially in Gram-negative bacteria.
Breakpoints
EUCAST clinical MIC breakpoints 2009 (2009-12-02, v 1):
For susceptibility testing purposes, the concentration of tazobactam is fixed at 4 mg/L
| Pathogen | Species-related breakpoints (S≤/R>) |
| Enterobacteriaceae | 8/16 |
| Pseudomonas | 16/16 |
| Gram-negative and Gram-positive anaerobes | 8/16 |
| Non-species related breakpoints | 4/16 |
The susceptibility of streptococci is inferred from the penicillin susceptibility.
The susceptibility of staphylococci is inferred from the oxacillin susceptibility.
Susceptibility
The prevalence of acquired resistance may vary geographically and with time for selected species and local information on resistance is desirable, particularly when treating severe infections. As necessary, expert advice should be sought when the local prevalence of resistance is such that the utility of the agent in at least some types of infections is questionable.
Groupings of relevant species according to piperacillin / tazobactam susceptibility
Commonly susceptible species
Gram positive aerobes
Enterococcus faecalis
Listeria monocytogenes
Staphylococcus aureus, methicillin susceptible£
Staphylococcus species, coagulase negative, methicillin-susceptible
Streptococcus pyogenes
Group B streptococci
Gram negative aerobes
Citrobacter koseri
Haemophilus influenzae
Moraxella catarrhalis
Proteus mirabilis
Gram positive anaerobes
Clostridium spp.
Eubacterium spp.
Peptostreptococcus spp.
Gram negative anaerobes
Bacteroides fragilis group
Fusobacterium spp.
Porphyromonas spp.
Prevotella spp.
Species for which acquired resistance may be a problem
Gram positive aerobes
Enterococcus faecium $,.+
Streptococcus pneumonia
Streptococcus viridans group
Gram negative aerobes
Actinobacter baumannii $
Burkholderia cepacia
Citrobacter freundii
Enterobacter spp.
Escherichia coli
Klebsiella pneumonia
Morganella morganii
Proteus vulgaris
Providencia ssp.
Pseudomonas aeruginosa
Serratia spp.
Inherently resistant organisms
Gram positive aerobes
Corynebacterium jeikeium
Gram negative aerobes Legionella spp
Stenotrophomonas maltophilia +,$
Other microorganisms
Chlamydophilia pneumonia
Mycoplasma pneumonia
$ Species showing natural intermediate susceptibility
+ Species for which high resistance rates (more than 50%) have been observed in one or more areas/countries/regions within the EU.
£ All methicillin-resistant staphylococci are resistant to piperacillin / tazobactam.