Should You Switch from Ertapenem to Imipenem-Cilastatin (or Meropenem)?
No, you should not switch from ertapenem to imipenem-cilastatin or meropenem solely because the organism is reported as "susceptible to imipenem." If the infection is caused by a susceptible organism and the patient is clinically improving on ertapenem, continuing ertapenem is appropriate and preferred from an antimicrobial stewardship perspective. 1
Understanding Carbapenem Susceptibility Reporting
Ertapenem susceptibility predicts imipenem/meropenem susceptibility for Enterobacteriaceae: When an organism (particularly ESBL-producing Enterobacteriaceae) is susceptible to ertapenem, it will be susceptible to imipenem and meropenem. 2
Laboratory reporting practices: Many microbiology laboratories report imipenem susceptibility as a class representative for carbapenems, but this does not mean imipenem is superior to ertapenem for susceptible organisms. 1
Equivalent clinical efficacy: Multiple studies demonstrate that ertapenem achieves equivalent clinical and microbiological outcomes compared to imipenem/meropenem for susceptible Enterobacteriaceae infections, including ESBL-producing strains. 3, 4, 5
When Ertapenem Is Appropriate
Continue ertapenem if:
The infection is community-acquired or healthcare-associated without risk factors for Pseudomonas aeruginosa or Enterococcus species. 6, 1
The patient is non-critically ill or has mild-to-moderate severity infection. 6
The organism is an ESBL-producing Enterobacteriaceae (E. coli, Klebsiella pneumoniae, Proteus mirabilis) without carbapenem resistance. 1, 2
The patient is clinically improving on current therapy. 3, 4
Source control has been achieved (for intra-abdominal infections). 6
When to Switch to Imipenem-Cilastatin or Meropenem
Switch to a Group 2 carbapenem (imipenem, meropenem) if:
Critically ill patients with severe physiologic disturbance, septic shock, or high-severity healthcare-associated infections requiring broader empiric coverage. 6
Documented or high-risk Pseudomonas aeruginosa infection: Ertapenem lacks antipseudomonal activity. 1, 2, 7
Documented or high-risk Enterococcus species infection: Ertapenem has limited enterococcal activity. 6, 1, 2
Nosocomial infections in patients with recent antibiotic exposure, prolonged ICU stay, or indwelling devices where multidrug-resistant organisms (MDROs) including Pseudomonas are likely. 6
Necrotizing soft tissue infections or mixed aerobic-anaerobic infections requiring maximal broad-spectrum coverage. 6
Clinical failure on ertapenem with persistent fever, worsening clinical parameters, or microbiological failure. 5
Antimicrobial Stewardship Considerations
Preserve Group 2 carbapenems: Ertapenem should be preferentially used when its spectrum is adequate to conserve imipenem and meropenem for infections requiring antipseudomonal activity. 6, 1
No increased Pseudomonas resistance: Multiple studies over 5+ years demonstrate that ertapenem use does not select for imipenem-resistant Pseudomonas aeruginosa. 8, 9
Equivalent outcomes in ESBL bacteremia: Even in critically ill patients with hypoalbuminemia, ertapenem demonstrates comparable clinical outcomes to meropenem for ESBL-producing Enterobacteriaceae bacteremia, though antibiotic escalation occurred more frequently. 5
Special Populations and Caveats
Critically ill patients with hypoalbuminemia: While one small study showed no difference in clinical failure between ertapenem and meropenem, there was higher antibiotic escalation with ertapenem (33% vs 3%). Consider meropenem if albumin <2.5 g/dL and severe sepsis. 5
Patients on valproic acid: All carbapenems reduce valproic acid levels, but ertapenem and meropenem have a greater effect (60-72% reduction) than imipenem-cilastatin (42% reduction). Avoid concurrent use or switch to alternative antibiotics. 10
Once-daily dosing advantage: Ertapenem's extended half-life allows once-daily administration, facilitating outpatient parenteral antimicrobial therapy (OPAT) and improving compliance. 1, 7
Clinical Decision Algorithm
Identify the organism and infection source: If ESBL-producing Enterobacteriaceae from urinary, intra-abdominal, or skin/soft tissue source → ertapenem is appropriate. 6, 1
Assess severity: Non-critically ill without septic shock → continue ertapenem. 6, 5
Evaluate for Pseudomonas/Enterococcus risk: No recent antibiotics, no ICU stay, no indwelling catheters → ertapenem is sufficient. 6, 1
Monitor clinical response: Improving fever curve, normalizing white blood cell count, resolving symptoms → continue ertapenem. 3, 4
Switch only if: Clinical deterioration, documented Pseudomonas/Enterococcus, or critical illness with shock. 6, 5