Carbapenems are broad spectrum beta lactam antibiotics which are often reserved antibiotics for selected serious infections. Examples include meropenem, imipenem and ertapenem. This article covers the spectrum of activity and clinical indications of carbapenems, their mechanism of action, pharmacokinetics, contraindications, adverse effects and clinically significant drug interactions. It also compares the properties of meropenem, imipenem/cilastatin and ertapenem, highlighting important differences in antimicrobial coverage, renal elimination and dosing. Spectrum of activity and Indications for Use Carbapenems are bactericidal agents which have activity against aerobic and anaerobic gram-positive and gram-negative organisms. Carbapenems are often reserved for serious infections caused by susceptible organisms, including certain extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales. They should not be used routinely when narrower-spectrum antibiotics are suitable. Addition of a hydroxyethyl side chain to the beta-lactam ring is responsible for carbapenems resistance against beta-lactamases. Imipenem and meropenem are used to treat infections such as hospital-acquired pneumonia, intra-abdominal infections, skin and soft-tissue infections and urinary tract infections. Meropenem can also be used in bacterial meningitis and febrile neutropenic patients. Ertapenem is not active against atypical respiratory pathogens but can be used to treat abdominal and gynaecological infections, for community-acquired pneumonia and skin and soft tissue infections. Ertapenem is administered once daily and is a common choice for treatment of susceptible infections at home with intravenous antibiotics. The table below describes general patterns of carbapenem activity. These are general patterns rather than guarantees of susceptibility. Carbapenem-resistant organisms may be encountered in all these groups, and the table should not replace local microbiology advice or susceptibility testing. Gram positive bacteria Gram negative bacteria Anaerobes Etrapenem ❌Meticillin-resistant Staphylococcus aureus (MRSA) ❌Enterococcus faecium ✅Streptococcus pneumoniae ✅Methicillin-susceptible-staphylococci (including Staphylococcus aureus) ❌Pseudomonas aeruginosa ❌Acinetobacter spp ✅Escherichia coli* ✅Haemophilus influenzae* ✅Klebsiella pneumoniae ❌Lactobacillus species ✅Clostridium species (excluding C. difficile)* Imipenem ❌Meticillin-resistant Staphylococcus aureus (MRSA) ❌Enterococcus faecium ✅Methicillin-susceptible-staphylococci (including Staphylococcus aureus) ❌ Legionella spp. ❌Stenotrophomonas maltophilia ✅ Pseudomonas aeruginosa ✅Escherichia coli ✅Haemophilus influenzae ✅Klebsiella pneumoniae ✅Bacteroides spp. (including B. fragilis) ✅Fusobacterium spp. (including F. nucleatum and F. necrophorum) ✅ Prevotella spp. (including P. melaninogenica, P. bivia, and P. buccae) Meropenem ❌Meticillin-resistant Staphylococcus aureus (MRSA) ✅ Enterococcus faecium* ✅Staphylococcus species (methicillin-susceptible) including ✅Staphylococcus epidermidis ✅Streptococcus pneumoniae ✅ Pseudomonas aeruginosa* ✅ Acinetobacter spp.* ✅Enterobacteriaceae* ✅Escherichia coli ✅Haemophilus influenzae ✅Clostridium perfringens ✅Peptoniphilus asaccharolyticus ✅Peptostreptococcus species (including P. micros, P anaerobius, P. magnus) *Resistance may occur to these species ❌ – not reliably active ✅ – usually active Mechanism of Action Carbapenems are bactericidal and inhibit bacterial cell wall synthesis in both gram-negative and gram-positive bacteria by binding to penicillin binding proteins (PBPs). This prevents cross linking peptidoglycans, weakening the cell walls and leading to bacterial cell swelling, lysis and ultimately death. Carbapenems resist many beta-lactamases, but carbapenemases can inactivate them. Created in BioRender. Boucher, M. (2026) https://BioRender.com/nbhjko8 Fig 1Mechanism of Action of Carbapenems Pharmacokinetics Most carbapenems are not orally active, therefore the table below describes the pharmacokinetics of intravenous carbapenems. Intravenous administration provides 100% bioavailability. Imipenem is given with cilastin, blocking its inactivation in the kidney. Imipenem can also be given with relebactam which is a beta-lactamase inhibitor. Carbapenems are primarily renally excreted and all require dose adjustment in renal impairment, in line with local guidance and manufacturer recommendations. Renal function is particularly important because accumulation can increase the risk of neurotoxicity and seizures. Distribution Metabolism Excretion Ertapenem Highly protein bound (92%-95%) Volume of distribution = 8L ~37% metabolised via hydrolysis of beta-lactam ring 80% renal, 10% faeces Imipenem Plasma protein binding 20%, Volume of distribution = 24.3L Extensively metabolised in kidneys by dehydropeptidase-I. Cilastatin inhibits this enzyme. Primarily excreted by kidneys When given with cilastatin, 63% of dose recovered in urine unchanged Meropenem Plasma protein binding 2% Good penetration Metabolised by hydrolysis to inactive metabolites Primarily renally excreted (70% unchanged, 28% metabolites) Contraindications Carbapenems are contraindicated in patients with a known serious hypersensitivity to the relevant medicine or its excipients, according to the product information. A history of immediate or severe hypersensitivity to penicillins, cephalosporins or other beta-lactams requires careful assessment because cross-reactivity is possible. Adverse Effects and Cautions Neurological Effects Beta lactam antibiotics can increase the risk of convulsions however meropenem is less likely to cause seizures and can be used in CNS infections. Ertapenem can also cause encephalopathy. Gastrointestinal Effects Carbapenems can commonly cause gastrointestinal upset. Due to the broad spectrum of activity they can also cause antibiotic associated colitis. Hypersensitivity and skin reactions Severe cutaneous adverse reactions (SCARs), including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), erythema multiforme (EM) and acute generalised exanthematous pustulosis (AGEP), have been reported with carbapenem use. Sodium Content of Meropenem Meropenem contains 4mmol (90mg) of sodium per 1g vial, therefore caution should be undertaken for patients on a low sodium diet. WHO recommends a maximum daily intake of 2g of sodium for an adult; a dose of 2g TDS represents 27% of the recommended daily intake. Other Adverse Effects Other reported adverse effects include: Rhabdomyolysis Drug induced liver injury can occur with meropenem and imipenem Rarely, meropenem can cause hypokalaemia Haematological abnormalities Interactions Carbapenems reduce valproate levels by up to 60-100% and the combination should be avoided or an alternative anticonvulsant needs to be prescribed. Seizures can occur when imipenem is administered with ganciclovir. Administration of antibiotics with warfarin may augment its anticoagulant effects; INR should be monitored. References Ritter JM, Flower RJ, Henderson G, Loke YK, MacEwan DJ. Rang & Dale’s Pharmacology. 9th ed. London: Elsevier; 2019. Hitchings BSc, M., Lonsdale, D., Burrage, D., Baker, E. (2022). The Top 100 Drugs – E-Book. Netherlands: Elsevier. Meropenem 1 g powder for solution for injection or infusion – Summary of Product Characteristics (SmPC) – (emc) | 5067 Ertapenem 1g Powder for Concentrate for Solution for Infusion – Summary of Product Characteristics (SmPC) – (emc) | 11161 Recarbrio 500 mg/500 mg/250 mg powder for solution for infusion – Summary of Product Characteristics (SmPC) – (emc) | 11675 Carbapenems | Treatment summaries | BNF | NICE Do you think you’re ready? Take the quiz below QuizPro Feature Carbapenems Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 More Questions Available Upgrade to TeachMePharmacy Pro Challenge yourself with over 400 multiple-choice questions to reinforce learning. Learn More Rate This Article