What are the considerations for using ertapenem (a carbapenem antibiotic) in a female patient of childbearing age with a bacterial infection in early pregnancy?

Ertapenem Use in Early Pregnancy

Ertapenem can be considered for use in early pregnancy when treating severe, recalcitrant bacterial infections that require carbapenem coverage, as animal studies showed no teratogenic evidence and the limited available human data are insufficient to establish harm, though it should be reserved for situations where narrower-spectrum, better-studied antibiotics are inadequate. 1, 2

Evidence Quality and Safety Profile

The FDA drug label explicitly states that available data from post-marketing cases with ertapenem use in pregnancy are insufficient to inform any drug-associated risks for major birth defects, miscarriage, or adverse maternal or fetal outcomes 2. However, the animal reproduction data provide some reassurance:

• In rats, intravenous ertapenem at doses up to 1.2 times the maximum recommended human dose (based on AUC) during organogenesis showed no maternal or embryofetal effects 2
• In mice, doses up to 3 times the MRHD (based on body surface area) showed only slight decreases in average fetal weight with decreased ossified sacrocaudal vertebrae, but no maternal effects 2
• Pre-postnatal studies in rats at 1.2 times the MRHD showed no fetal toxicity, developmental delays, or impaired reproduction in first generation offspring 2

Clinical Context for Use

The 2025 North American guidelines for hidradenitis suppurativa in special populations acknowledge that data on ertapenem in pregnancy are extremely limited, but the absence of teratogenic evidence in animal studies allows consideration in select recalcitrant cases 1. This represents expert consensus that ertapenem occupies a niche role when other options have failed.

For maternal sepsis, the 2025 Mayo Clinic guidelines propose ertapenem as an alternative to conventional peripartum antibiotic regimens, offering reliable coverage for gram-positive, gram-negative, and anaerobic bacteria with a favorable adverse effect profile 1. However, this recommendation comes with important caveats about enterococcal coverage (see below).

Spectrum of Activity Considerations

Ertapenem provides broad-spectrum coverage against Enterobacteriaceae (including ESBL-producers), gram-positive aerobes, and anaerobes, but lacks reliable activity against Enterococcus species, Pseudomonas aeruginosa, and atypical organisms (Mycoplasma, Ureaplasma) 1, 3, 4, 5.

The clinical significance of this coverage gap depends on the infection type:

• For complicated intra-abdominal infections, acute pelvic infections, and complicated UTIs in pregnancy, the Mayo Clinic guidelines note that despite frequent isolation of atypical organisms, clinical outcomes are not worse when these organisms are not specifically targeted 1
• Enterococcus coverage is lacking with ertapenem, but the role of these organisms in peripartum infections remains unclear 1

Practical Algorithm for Decision-Making

Use ertapenem in early pregnancy when:

1. The patient has a severe bacterial infection requiring parenteral therapy
2. The infection is caused by or suspected to involve ESBL-producing Enterobacteriaceae or multidrug-resistant gram-negative organisms 6
3. Narrower-spectrum options (penicillins, cephalosporins) are contraindicated due to allergy or documented resistance
4. The infection does not require coverage of Pseudomonas, Enterococcus, or atypical organisms 1, 3

Avoid ertapenem when:

• First-line pregnancy-safe antibiotics (amoxicillin, cephalexin, penicillin G, ampicillin) are appropriate 7
• The infection requires Pseudomonas or Enterococcus coverage 1, 4
• Community-acquired infections can be treated with ceftriaxone or other narrower-spectrum agents 1

Dosing and Administration

Standard dosing is 1 gram IV or IM once daily, which is the same regimen used in non-pregnant adults 3, 4, 5. The once-daily dosing is enabled by ertapenem's high protein binding (95%) and 4-hour half-life 4, 5.

Clinical Efficacy Data

While not pregnancy-specific, ertapenem demonstrated 84-94% clinical response rates across multiple infection types (complicated intra-abdominal infections, complicated skin/soft tissue infections, complicated UTIs, community-acquired pneumonia, acute pelvic infections) with efficacy equivalent to piperacillin-tazobactam and ceftriaxone plus metronidazole 3, 5, 8.

Critical Pitfalls to Avoid

• Do not use ertapenem as first-line therapy when narrower-spectrum pregnancy-safe antibiotics are appropriate – reserve it for resistant organisms or severe infections 1, 7
• Do not assume ertapenem covers Enterococcus or Pseudomonas – if these organisms are suspected, alternative regimens are required 1, 4
• Do not use ertapenem for meningitis – CSF penetration is insufficient 2
• Remember that ertapenem lacks atypical coverage – if Mycoplasma or Ureaplasma are concerns (though their clinical significance in peripartum infections is unclear), consider adding azithromycin 1

Breastfeeding Considerations

Ertapenem is present in human milk at low concentrations (< 0.13 to 0.38 mcg/mL within 24 hours of the last dose), becoming undetectable by day 5 after discontinuation 2. The developmental and health benefits of breastfeeding should be weighed against the mother's clinical need for ertapenem 2.