Are Cefdinir (Cefdinir) and Rocephin (Ceftriaxone) effective against Enterococcus faecalis?

Cefdinir and Rocephin Do Not Adequately Cover Enterococcus faecalis

Neither cefdinir (oral third-generation cephalosporin) nor ceftriaxone (Rocephin, parenteral third-generation cephalosporin) provides adequate coverage against Enterococcus faecalis when used alone. This is a critical limitation when treating infections potentially caused by this organism.

Enterococcus faecalis and Cephalosporin Resistance

Enterococci, including E. faecalis, demonstrate intrinsic resistance to cephalosporins due to:

• Low affinity of penicillin-binding proteins for cephalosporins
• Poor penetration of cephalosporins through the enterococcal cell wall
• Expression of low-affinity penicillin-binding proteins (PBPs)

Evidence from Guidelines

The 2005 practice parameter update from the Journal of Allergy and Clinical Immunology explicitly states that "cephalosporins and antistaphylococcal penicillins (oxacillin, nafcillin) have minimal or no in vitro activity against enterococci" 1. This clearly indicates that cefdinir, as a third-generation cephalosporin, would be ineffective against E. faecalis.

Effective Treatment Options for E. faecalis

For infections caused by E. faecalis, the following options are recommended:

First-line options:

• Ampicillin or penicillin G (drug of choice for susceptible strains)
• Ampicillin plus gentamicin (for serious infections requiring synergistic bactericidal activity)
• Ampicillin plus ceftriaxone (as a combination therapy only, not as monotherapy with ceftriaxone)

For resistant strains:

• Vancomycin (for ampicillin-resistant, vancomycin-susceptible strains)
• Linezolid or daptomycin (for vancomycin-resistant enterococci) 1

The Ampicillin-Ceftriaxone Combination Paradox

While ceftriaxone alone is ineffective against E. faecalis, the combination of ampicillin plus ceftriaxone demonstrates synergistic activity against E. faecalis through saturation of different penicillin-binding proteins 1. This combination has become an accepted alternative for treating E. faecalis infections, particularly in patients who cannot tolerate aminoglycosides.

A pilot study demonstrated that the ampicillin-ceftriaxone combination was effective in treating orthopedic infections due to E. faecalis, with a 90% cure rate 2. Similarly, a study of E. faecalis endocarditis showed the combination to be effective for high-level aminoglycoside-resistant E. faecalis 3.

Clinical Implications

When treating infections where E. faecalis is a concern:

1. Do not rely on cefdinir or ceftriaxone as monotherapy
2. Consider ampicillin as the cornerstone of therapy
3. For serious infections:
   • Use ampicillin plus gentamicin (traditional approach)
   • Or ampicillin plus ceftriaxone (alternative for patients with renal concerns)

Common Pitfalls to Avoid

1. Misinterpreting synergy data: While ampicillin-ceftriaxone shows synergy, this does not mean ceftriaxone alone has activity against E. faecalis
2. Assuming all enterococci behave the same: E. faecalis and E. faecium may have different susceptibility patterns
3. Overlooking the need for susceptibility testing: Always obtain susceptibility testing before initiating definitive therapy for enterococcal infections

For empiric coverage of infections where E. faecalis is a concern (such as complicated urinary tract or intra-abdominal infections), ampicillin should be included in the regimen if cephalosporins are used 1.