Does cefdinir cover Staphylococcus aureus, including methicillin‑resistant Staphylococcus aureus (MRSA)?

Cefdinir Coverage of Staphylococcus aureus

Cefdinir provides reliable coverage against methicillin-susceptible Staphylococcus aureus (MSSA) but has NO activity against methicillin-resistant Staphylococcus aureus (MRSA). 1

Spectrum Against Staphylococcal Species

Methicillin-Susceptible Staphylococcus aureus (MSSA)

• Cefdinir is FDA-approved and clinically effective for MSSA infections, with 100% susceptibility rates in contemporary surveillance studies. 1, 2
• The drug demonstrates potent activity with MIC₅₀/₉₀ values of 0.5/0.5 mcg/mL against oxacillin-susceptible S. aureus strains. 2
• Cefdinir is 4- to 16-fold more potent than cephalexin against staphylococci, making it superior to first-generation oral cephalosporins. 3
• The FDA label explicitly states cefdinir is active against "Staphylococcus aureus (methicillin-susceptible strains only)." 1

Methicillin-Resistant Staphylococcus aureus (MRSA)

• Cefdinir is completely inactive against MRSA and should never be used for suspected or confirmed MRSA infections. 1
• The FDA label specifically excludes methicillin-resistant staphylococci from cefdinir's spectrum of activity. 1
• For MRSA coverage, vancomycin, linezolid, daptomycin, or ceftaroline (the only cephalosporin with MRSA activity) must be used instead. 4, 5

Other Staphylococcal Species

• Cefdinir shows excellent activity against methicillin-susceptible coagulase-negative staphylococci (MIC₅₀/₉₀ of 0.06/0.12 mcg/mL, 100% susceptibility). 2
• The drug is active against S. epidermidis (methicillin-susceptible strains only) with MIC₉₀ values of 0.06 mg/L. 1, 6

Clinical Positioning in Guidelines

Appropriate Use for Staphylococcal Infections

• Cefdinir is recommended as a suitable agent for uncomplicated skin and soft tissue infections caused by MSSA. 4, 7
• The 2005 sinusitis guidelines identify cefdinir as appropriate for infections where S. aureus is a likely pathogen (alongside S. pneumoniae and H. influenzae). 4
• Cefdinir maintains bactericidal activity against MSSA with post-antibiotic effects ranging from 0.8 to 1 hour. 6

When NOT to Use Cefdinir

• Never use cefdinir empirically when MRSA is suspected or prevalent in your community, particularly for nosocomial infections or in critically ill patients. 4
• In healthcare-associated infections where MRSA prevalence is 30-66%, broad-spectrum agents with MRSA coverage are essential. 4
• For serious MSSA infections requiring parenteral therapy, cefazolin or nafcillin/oxacillin are preferred over oral cefdinir. 8

Important Clinical Caveats

Resistance Patterns

• Cefdinir is inactive against oxacillin-resistant staphylococci through alteration of penicillin-binding proteins. 1
• Development of resistance during therapy is rare, occurring at frequencies of 2 × 10⁻⁹ with S. epidermidis. 6

Dosing Considerations

• Standard adult dosing is 300 mg twice daily or 600 mg once daily for 10 days for skin infections. 1
• Dosage adjustment is required when creatinine clearance is <30 mL/min (reduce to 300 mg once daily). 1

Common Pitfalls to Avoid

• Do not assume all third-generation cephalosporins have similar staphylococcal coverage—cefixime and ceftibuten have poor activity against S. pneumoniae and should not be used for respiratory infections, while cefdinir maintains good gram-positive coverage. 4
• Do not use cefdinir for polymicrobial infections requiring anaerobic coverage without adding metronidazole. 4
• Remember that cefdinir is significantly more potent than cephalexin (4- to 64-fold depending on pathogen), so they are not interchangeable. 2