| Pharmacotherapeutic group: antibacterials for systemic use, carbapenems, ATC code: J01DH02 Mode of action Meropenem exerts its bactericidal activity by inhibiting bacterial cell wall synthesis in Gram-positive and Gram-negative bacteria through binding to penicillin-binding proteins (PBPs).Pharmacokinetic/Pharmacodynamic (PK/PD) relationship
Similar to other beta-lactam antibacterial agents, the time that meropenem concentrations exceed the MIC (T>MIC) has been shown to best correlate with efficacy. In preclinical models meropenem demonstrated activity when plasma concentrations exceeded the MIC of the infecting organisms for approximately 40 % of the dosing interval. This target has not been established clinically.Mechanism of resistance Bacterial resistance to meropenem may result from: (1) decreased permeability of the outer membrane of Gram-negative bacteria (due to diminished production of porins) (2) reduced affinity of the target PBPs (3) increased expression of efflux pump components, and (4) production of beta-lactamases that can hydrolyse carbapenems. Localised clusters of infections due to carbapenem-resistant bacteria have been reported in the European Union.There is no target-based cross-resistance between meropenem and agents of the quinolone, aminoglycoside, macrolide and tetracycline classes. However, bacteria may exhibit resistance to more than one class of antibacterials agents when the mechanism involved include impermeability and/or an efflux pump(s).Breakpoints European Committee on Antimicrobial Susceptibility Testing (EUCAST) clinical breakpoints for MIC testing are presented below. | EUCAST clinical MIC breakpoints for meropenem (2009-06-05, v 3.1)
| | Organism
| Susceptible (S) (mg/l)
| Resistant (R) (mg/l)
| | Enterobacteriaceae | 2
| > 8
| | Pseudomonas | 2
| > 8
| | Acinetobacter | 2
| > 8
| | Streptococcus
groups A, B, C, G | 2
| > 2
| | Streptococcus pneumoniae1 | 2
| > 2
| | Other streptococci
| 2
| 2
| | Enterococcus | --
| --
| | Staphylococcus2 | note 3
| note 3
| | Haemophilus influenzae1
and Moraxella catarrhalis | 2
| > 2
| | Neisseria meningitidis2,4 | 0.25
| > 0.25
| | Gram-positive anaerobes
| 2
| > 8
| | Gram-negative anaerobes
| 2
| > 8
| | Non-species related breakpoints5 | 2
| > 8
|
1
Meropenem breakpoints for Streptococcus pneumoniae and Haemophilus influenzae in meningitis are 0.25/1 mg/L. 2
Strains with MIC values above the S/I breakpoint are rare or not yet reported. The identification and antimicrobial susceptibility tests on any such isolate must be repeated and if the result is confirmed the isolate sent to a reference laboratory. Until there is evidence regarding clinical response for confirmed isolates with MIC above the current resistant breakpoint (in italics) they should be reported as resistant. 3
Susceptibility of staphylococci to meropenem is inferred from the methicillin susceptibility. 4
Meropenem breakpoints in Neisseria meningitidis
relates to meningitis only. 5
Non-species related breakpoints have been determined mainly from PK/PD data and are independent of the MIC distributions of specific species. They are for use for species not mentioned in the table and footnotes. --
= Susceptibility testing not recommended as the species is a poor target for therapy with the medicinal product. 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.The following table of pathogens listed is derived from clinical experience and therapeutic guidelines.| Commonly susceptible species | | Gram-positive aerobes | | Enterococcus faecalis$ | | Staphylococcus aureus
(methicillin-susceptible) £ | | Staphylococcus
species (methicillin-susceptible) including Staphylococcus epidermidis | | Streptococcus agalactiae
(Group B) | | Streptococcus milleri
group (S. anginosus, S. constellatus, and S. intermedius) | | Streptococcus pneumoniae | | Streptococcus pyogenes
(Group A) | | | | Gram-negative aerobes | | Citrobacter freudii | | Citrobacter koseri | | Enterobacter aerogenes | | Enterobacter cloacae | | Escherichia coli | | Haemophilus influenzae | | Klebsiella oxytoca | | Klebsiella pneumoniae | | Morganella morganii | | Neisseria meningitidis | | Proteus mirabilis | | Proteus vulgaris | | Serratia marcescens | | | | Gram-positive anaerobes | | Clostridium perfringens | | Peptoniphilus asaccharolyticus | | Peptostreptococcus
species (including P. micros, P anaerobius, P. magnus) | | | | Bacteroides caccae | | Bacteroides fragilis group | | Prevotella bivia | | Prevotella disiens | | | | Species for which acquired resistance may be a problem | | Gram-positive aerobes | | Enterococcus faecium$ | | | | Gram-negative aerobes | | Acinetobacter
species | | Burkholderia cepacia | | Pseudomonas aeruginosa | | | | Inherently resistant organisms | | Gram-negative aerobes | | Stenotrophomonas maltophilia | | Legionella
species | | | | Other micro-organisms | | Chlamydophila pneumoniae | | Chlamydophila psittaci | | Coxiella burnetii | | Mycoplasma pneumoniae |
$Species that show natural intermediate susceptibility £All methicillin-resistant staphylococci are resistant to meropenem Resistance rate 50% in one or more EU countries. | |