Is Enterococcus faecalis in the urine susceptible to cefdinir (Omnicef)?

Enterococcus faecalis in Urine is NOT Susceptible to Cefdinir

Enterococcus faecalis in urinary tract infections is not susceptible to cefdinir (Omnicef) and this antibiotic should not be used for treating E. faecalis UTIs. 1 According to the FDA drug information, cefdinir is specifically listed as inactive against Enterococcus species.

Mechanism of Resistance

Enterococcus species have intrinsic resistance to cephalosporins including cefdinir due to:

• Low affinity of penicillin-binding proteins (PBPs) for cephalosporins
• Poor penetration of cephalosporins through the enterococcal cell wall
• Expression of β-lactamases in some strains

The FDA drug label explicitly states: "Cefdinir is inactive against most strains of Enterobacter spp., Pseudomonas spp., Enterococcus spp., penicillin-resistant streptococci, and methicillin-resistant staphylococci." 1

Recommended Treatment Options for E. faecalis UTIs

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

1. Nitrofurantoin - 100 mg PO every 6 hours (avoid if CrCl <30 mL/min) 2
2. Fosfomycin - Single dose of 3 g PO 2
3. Ampicillin/Amoxicillin - 500 mg PO/IV every 8 hours 2

For complicated E. faecalis UTIs or in cases of vancomycin-resistant enterococci (VRE):

1. Linezolid - 600 mg IV or PO every 12 hours 2
2. High-dose daptomycin - 8-12 mg/kg/day (for bloodstream infections) 2

Antimicrobial Susceptibility Patterns

E. faecalis typically shows better susceptibility profiles than E. faecium:

• E. faecalis generally remains susceptible to ampicillin, nitrofurantoin, and often vancomycin 3
• Both E. faecalis and E. faecium show increasing resistance to high-level gentamicin 3
• Vancomycin resistance is increasing in enterococci, with higher rates in E. faecium than E. faecalis 2

Clinical Considerations

• Always obtain urine culture and susceptibility testing before initiating targeted therapy for E. faecalis UTIs 4
• Consider the source of infection - studies show that 15.8-26.9% of E. faecalis UTIs may be endogenous (from the patient's own intestinal tract) 5
• For catheter-associated UTIs with E. faecalis, catheter removal or exchange should be performed when possible 4
• Nitrofurazone-impregnated catheters have shown significant reduction in E. faecalis biofilm formation compared to other catheter types 6

Treatment Duration

• For uncomplicated lower UTIs: 5-7 days of appropriate therapy 4
• For complicated UTIs: 10-14 days of appropriate therapy 4

Common Pitfalls to Avoid

1. Using cephalosporins for enterococcal infections - Enterococci are intrinsically resistant to most cephalosporins including cefdinir 1
2. Failing to obtain susceptibility testing - Increasing resistance patterns necessitate culture-guided therapy 3
3. Overlooking catheter removal - Biofilm formation on catheters can lead to persistent infection 6
4. Inadequate duration of therapy - Complicated enterococcal UTIs require longer treatment courses 4

In conclusion, when treating urinary tract infections caused by Enterococcus faecalis, cefdinir is not an appropriate choice due to intrinsic resistance. Alternative agents such as nitrofurantoin, fosfomycin, or ampicillin should be selected based on susceptibility testing.