Imipenem vs Meropenem

Imipenem chemical structure
Imipenem monohydratre
meropenem trihydrate chemical structure
Meropenem Trihydrate

What They Have In Common

Both imipenem and meropenem belong to the carbapenem family.

They look pretty much the same: both of them are off-white to slight yellowish crystalline powder.

If you put both samples together, you will not be able to tell which is which by their character.

Both of them share the attributes of Carbapenems:

1. Wide antibacterial spectrum

Strong antibacterial activity against various G+, G- and anaerobic bacteria, poor antibacterial effect against methicillin-resistant Staphylococcus and maltophilic narrow-feeding Staphylococcus, etc., ineffective against fungi.

2. Strong antibacterial effects

Carbapenems are tightly bound to PBPs (penicillin-binding proteins).

3. Stable to β-lactamases

Antibiotic after-effects (on G+ and G- bacteria), etc.

4. Wide clinical indications are determined by the antimicrobial spectrum

4.1 Severe infections caused by multi-resistant but drug-susceptible aerobic gram-negative bacilli

4.2 Mixed infections of anaerobic and aerobic bacteria such as Bacteroides fragilis

4.3 Empirical treatment of severe infections in immunodeficient patients whose pathogenic organisms have not been identified.

However, their clinical uses require special attention

#1. They are contraindicated in patients with hypersensitivity to this class of drugs and their companion components

#2. Not indicated for the treatment of mild infections, much less as prophylaxis.

#3. Patients with neurological infections who are indicated for meropenem or panipenem should still be closely monitored for the development of convulsions.

#4. Patients with renal insufficiency and elderly patients should reduce the dosage according to the degree of renal decompensation.

#5. The Carbapenem family is a super broad-spectrum antibiotic. Its long-term application is prone to fungal infections and can also cause antibiotic diarrhea.

Below is a video about the working mechanism of carbapenems.

Their Differences

As we see from their chemical structure, they have partial components as the same, their structural different parts are linked through the atom S.

Chemically speaking, the different parts of their structure have decided they will exert their own characters from the beginning.

Today we will break down their differences point by point, such as antimicrobial spectrum, mechanism of action, pharmacodynamics and pharmacokinetics, clinical efficacy, etc, so you guys can get it once and for all.

#1. Birthday and time to market

Imipenem was first patented in 1975 and not marketed in the USA till 1985. (trade name Primaxin along with others)

Meropenem was patented in 1983. It was first approved for medical use in Italy in 1995. (Marketed as Merrem among others)

One year later in 1996, it was approved in the USA.

#2. Antibacterial activity

The structural differences between the imipenem and meropenem are mainly in the structures attached to the C1 and C2 positions.

Thus, their antibacterial activities against G+ bacteria, Pseudomonas aeruginosa (PA), etc are different.

2.1 Staphylococcus and Enterococcus spp bacteria


2.2 Enterobacteriaceae bacteria


2.3 Pseudomonas aeruginosa


2.4 Anaerobic bacteria


#3. Drug tolerance

MRSA, maltophilia, Burkholderia cepacia, and Enterococcus faecalis have similar resistances to imipenem and meropenem.

#4. Stability after administration

Imipenem has the H-atom at position C1, which is easily degraded by p-renal dehydrogenase and must be combined with an enzyme inhibitor (cilastatin sodium) to avoid its metabolism in the kidney.

Therefore, to make sure the imipenem has stable efficacy, it must be combined with Cilastatin Sodium.

Meropenem has methyl (-CH3) at the C1 position, which is stable to renal dehydrogenase and does not require any enzyme inhibitors.

#5. Indications

Indications for imipenem include:

bacterial endocarditis (caused by MSSA), sepsis, skin, and soft tissue infections; lower respiratory tract infections; gynecologic infections; intra-abdominal infections; multipathogenic infections; uncomplicated and complicated urinary tract infections; gas gangrene, diabetic foot infections, bone/joint infections.

Indications for meropenem include:

1. Abdominal infections (appendicitis and peritonitis) caused by Streptococcus straw green, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, S. fragilis, S. polymorpha and Streptococcus pepticus

2. Meningitis caused by Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis (children three months or older)

3. Complicated skin and soft tissue infections caused by Staphylococcus aureus (MSSA only), Streptococcus pyogenes, Streptococcus aureus, Streptococcus lactis, Streptococcus griseus, Enterococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, Proteus mirabilis, Streptococcus fragilis, and Streptococcus peptidis

#6. Regular dose for adults


Mild to moderate infections: 0.25-0.5g IV q6h.

Urinary tract infections: 0.5g IV q6-8h

Severe or pseudomonas infections: 1g IV q6-8h

Obese patients: 1g IV q6h is recommended, but no clinical data are available.


Mild to moderate infections: 1 dose of 1 g every 8 hours administered intravenously.

severe infections and CNS infections: intravenous administration of 1 dose of 2 g every 8 hours

obese patients: intravenous administration of 1 dose of 2 g every 8 hours (limited data).

With ↑ PK/PD parameters, some experts recommend an extended infusion (>4h) for the treatment of severe infections and/or for the treatment of moderately resistant microorganisms (in combination with aminoglycosides).

These points above are pretty much what we know about the differences and similarities between imipenem and meropenem.

If you have different opinions, you are welcome to contact us anytime.


Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top