Antimicrobials · Carbapenems
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Ertapenem is a carbapenem antibiotic that lacks activity against Pseudomonas aeruginosa, Acinetobacter species, and Enterococcus species.
The primary clinical utility of ertapenem is the treatment of extended-spectrum beta-lactamase (ESBL) producing Enterobacteriaceae.
Ertapenem is administered via once-daily dosing due to its long serum half-life and high protein binding.
Like all carbapenems, ertapenem carries a risk of lowering the seizure threshold, particularly in patients with underlying CNS pathology or renal impairment.
Ertapenem is a beta-lactam antibiotic that functions by binding to penicillin-binding proteins (PBPs) to inhibit bacterial cell wall synthesis.
Patients with a severe IgE-mediated hypersensitivity (anaphylaxis) to penicillins or cephalosporins should avoid ertapenem due to the risk of cross-reactivity.
Ertapenem is frequently utilized for polymicrobial intra-abdominal infections and diabetic foot infections where coverage of anaerobes is required.
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A 68-year-old male with a history of type 2 diabetes mellitus presents with a non-healing ulcer on his left heel. Physical examination reveals purulent drainage, erythema extending 4 cm from the wound, and exposed bone upon probing. The patient is hemodynamically stable and has no known drug allergies. Blood cultures are pending, but wound cultures from a previous admission grew ESBL-producing E. coli and Bacteroides fragilis.
Which of the following is the most appropriate empiric antibiotic therapy for this patient?
Ertapenem
The patient has a diabetic foot infection requiring coverage for ESBL-producing organisms and anaerobes; ertapenem is the drug of choice for ESBL coverage while providing excellent anaerobic activity.
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Classification
Carbapenem antibiotic; lacks activity against Pseudomonas and Acinetobacter.
Indications
Intra-abdominal infections, complicated skin/soft tissue infections, community-acquired pneumonia.
Mechanism of Action
Binds penicillin-binding proteins (PBPs), inhibiting bacterial cell wall synthesis.
Side Effects
Diarrhea, nausea, seizures, anaphylaxis.
Contraindications / Monitoring
History of anaphylaxis to beta-lactams. Renal function (CrCl).
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Mechanism of Action
Ertapenem binds to penicillin-binding proteins (PBPs), specifically PBP 2 and 3, disrupting the final stage of peptidoglycan synthesis. This leads to cell lysis and death. It is highly stable against most beta-lactamases, including extended-spectrum beta-lactamases (ESBLs).
Unique Properties
Unlike other carbapenems (imipenem, meropenem), ertapenem has a long half-life allowing for once-daily dosing. Crucially, it is the only carbapenem that lacks activity against Pseudomonas aeruginosa and Acinetobacter species.
Indications
Indicated for complicated intra-abdominal infections, complicated skin and skin structure infections, and community-acquired pneumonia. It is also used for diabetic foot infections and as prophylaxis for colorectal surgery.
Pharmacokinetics
Ertapenem is highly protein-bound (95%), which contributes to its long half-life. It is primarily excreted via the kidneys; dosage adjustments are required for patients with CrCl < 30 mL/min.
Side Effects & Adverse Events
Common adverse effects include diarrhea, nausea, and headache. Seizures are a rare but serious risk, particularly in patients with underlying CNS disorders or renal impairment. Anaphylaxis and Clostridioides difficile-associated diarrhea are potential severe complications.
Contraindications
Hypersensitivity to any carbapenem or history of severe anaphylaxis to any beta-lactam antibiotic. Use with extreme caution in patients with a history of seizures or other CNS disorders due to the risk of lowering the seizure threshold.
Monitoring
Monitor renal function (serum creatinine and CrCl) to adjust dosing. Observe for signs of superinfection or C. difficile colitis (persistent diarrhea).
Clinical Pearls
Remember the Ertapenem spectrum gap: it covers ESBL-producing organisms but fails to cover Pseudomonas. If a board question describes an ESBL infection but the patient is stable and needs once-daily outpatient therapy, Ertapenem is the classic answer.