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 (2013-02-11, v 3.1 )
| Organism | Susceptible (S) (mg/l) | Resistant (R) (mg/l) |
| Enterobacteriaceae | ≤2 | >8 |
| Pseudomonas spp. | ≤2 | >8 |
| Acinetobacter spp. | ≤2 | >8 |
| Streptococcus groups A, B, C and G | note 6 | note 6 |
| Streptococcus pneumoniae1 | ≤2 | >2 |
| Viridans group streptococci2 | ≤2 | >2 |
| Enterococcus spp | -- | -- |
| Staphylococcus spp | note 3 | note 3 |
| Haemophilus influenzae1, 2 and Moraxella catarrhalis2 | ≤ 2 | > 2 |
| Neisseria meningitidis2,4 | ≤ 0.25 | > 0.25 |
| Gram-positive anaerobes except Clostridium difficile | ≤ 2 | > 8 |
| Gram-negative anaerobes | ≤ 2 | > 8 |
| Listeria monocytogenes | ≤ 0.25 | > 0.25 |
| Non-species related breakpoints5 | ≤ 2 | > 8 |
1Meropenem breakpoints for Streptococcus pneumoniae and Haemophilus influenzae in meningitis are 0.25 mg (Susceptible) and 1 mg/l (Resistant).
2 Isolates with MIC values above the susceptible breakpoint are very 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 values above the current resistant breakpoint they should be reported as resistant.
3Susceptibility of staphylococci to Carbepenem is inferred from the cefoxitinsusceptibility.
4 Breakpoints relate to meningitis only.
5Non-species related breakpoints have been determined using PK/PD data and are independent of MIC distributions of specific species. They are for use only for organisms that do not have specific breakpoints. Non species related breakpoints are based on the following dosages: EUCAST breakpoints apply to meropenem 1000 mg x 3 daily administered intravenously over 30 minutes as the lowest dose. 2 g x 3 daily was taken into consideration for severe infections and in setting the I/R breakpoint.
6 The beta-lactam susceptibility of streptococcus groups A, B, C and G is inferred from the penicillin susceptibility.
-- = Susceptibility testing not recommended as the species is a poor target for therapy with the drug. Isolates may be reported as R without prior testing.
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)
Gram-negative anaerobes
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.
Glanders and melioidosis: Use of meropenem in humans is based on in vitro B.mallei and B. pseudomallei susceptibility data and on limited human data. Treating physicians should refer to national and/or international consensus documents regarding the treatment of glanders and melioidosis.