Will Cefdinir provide sufficient coverage for Enterococcus Faecalis with sensitivities to Ampicillin and Nitrofurantoin (Macrobid)?

Cefdinir Does Not Provide Coverage for Enterococcus Faecalis

Cefdinir will not provide sufficient coverage for Enterococcus faecalis, even when the organism shows sensitivity to ampicillin and nitrofurantoin (Macrobid). 1

Why Cefdinir Is Ineffective Against Enterococci

Cefdinir, like other cephalosporins, has specific limitations in its antimicrobial spectrum:

• The FDA drug label explicitly states that cefdinir is "inactive against most strains of Enterococcus spp." 1
• The American Academy of Allergy and Clinical Immunology confirms that cephalosporins have minimal to no in vitro activity against enterococci 2
• Cefdinir is a third-generation oral cephalosporin that provides good coverage against common respiratory pathogens like Haemophilus influenzae, Moraxella catarrhalis, and penicillin-susceptible Streptococcus pneumoniae, but not enterococci 3

Appropriate Treatment Options for Enterococcus Faecalis

For Enterococcus faecalis infections, the following treatment options are recommended:

1. First-line therapy: Ampicillin or penicillin (when susceptible) 4

   • Ampicillin 200 mg/kg/day IV in 4-6 doses is the preferred treatment for susceptible strains

2. For uncomplicated infections: Nitrofurantoin (Macrobid) can be effective for urinary tract infections caused by susceptible strains

3. For more serious infections: Combination therapy may be required

   • Ampicillin plus ceftriaxone is recommended for serious infections like endocarditis 4
   • This combination demonstrates synergistic activity against E. faecalis through saturation of different penicillin-binding proteins 2

Important Clinical Considerations

• The ampicillin-ceftriaxone combination has been shown to be as effective as ampicillin-gentamicin for treating E. faecalis infections, with significantly less nephrotoxicity 4, 5

• Recent research shows that the synergistic effect of beta-lactam combinations against E. faecalis is dependent on the MICs of the organisms:

  • Isolates with higher penicillin MICs (4 μg/mL) and ceftriaxone MICs (≥512 μg/mL) show less synergy 6
  • For E. faecium (a different enterococcal species), the ampicillin-ceftriaxone combination does not provide uniform synergy 7

• For empiric coverage of infections where E. faecalis is a concern, ampicillin should be included in the regimen if cephalosporins are used 2

Bottom Line for Clinical Practice

If treating an infection caused by Enterococcus faecalis:

1. Do not rely on cefdinir alone, regardless of in vitro susceptibility results to other agents
2. Use ampicillin for susceptible strains (as indicated by your susceptibility testing)
3. Consider nitrofurantoin for uncomplicated urinary tract infections
4. For serious infections, consider combination therapy with ampicillin plus ceftriaxone

Remember that susceptibility to ampicillin and nitrofurantoin does not translate to susceptibility to cephalosporins like cefdinir due to intrinsic resistance mechanisms in enterococci.