Is meropenem effective against Staphylococcus aureus (Staph aureus)?

Meropenem Effectiveness Against Staphylococcus aureus

Meropenem has activity against methicillin-susceptible Staphylococcus aureus (MSSA) but is NOT effective against methicillin-resistant Staphylococcus aureus (MRSA) and should not be used as monotherapy for MRSA infections. 1, 2

Spectrum of Activity

MSSA Coverage

• Meropenem is FDA-approved and recommended for complicated skin and skin structure infections caused by methicillin-susceptible S. aureus isolates only 2
• The IDSA/ATS guidelines explicitly list meropenem as an appropriate empiric agent when MSSA coverage (without MRSA coverage) is indicated for hospital-acquired pneumonia 1
• Meropenem demonstrates bactericidal activity against MSSA, though it is slightly less active against staphylococci compared to imipenem 3

MRSA Resistance

• Methicillin-resistant staphylococci are uniformly resistant to meropenem 3
• The FDA label specifically states meropenem is indicated only for "methicillin-susceptible isolates" of S. aureus 2
• When MRSA coverage is required, vancomycin or linezolid must be added to the regimen 1

Clinical Application Algorithm

When to Use Meropenem for Staph aureus:

Step 1: Determine methicillin susceptibility

• If MSSA confirmed by culture → meropenem is appropriate 2
• If MRSA confirmed or suspected → meropenem is NOT adequate; add vancomycin or linezolid 1

Step 2: Assess infection severity and site

• For complicated skin/soft tissue infections with MSSA: meropenem 500 mg IV every 8 hours 2
• For severe infections or when P. aeruginosa co-infection possible: meropenem 1 gram IV every 8 hours 2
• For hospital-acquired pneumonia without MRSA risk factors: meropenem 1 gram IV every 8 hours provides MSSA coverage 1

Step 3: Consider empiric MRSA coverage if:

• IV antibiotics used in prior 90 days 1
• Unit prevalence of MRSA among S. aureus isolates >20% 1
• High mortality risk (septic shock, need for ventilatory support) 1
• Prior MRSA colonization or infection 1

Important Caveats

Combination Therapy Considerations

• Research demonstrates synergistic activity when meropenem is combined with vancomycin against MRSA in vitro 4, 5, 6
• However, clinical guidelines do not recommend meropenem monotherapy for MRSA regardless of in vitro synergy data 1
• If MRSA coverage is needed, use vancomycin or linezolid as the primary anti-MRSA agent, with meropenem providing gram-negative coverage 1

Dosing Adjustments

• Reduce dose in renal impairment: for CrCl 26-50 mL/min, give recommended dose every 12 hours; for CrCl 10-25 mL/min, give half dose every 12 hours 2
• Administer as IV infusion over 15-30 minutes, or 1 gram doses may be given as bolus over 3-5 minutes 2

Common Pitfall

• Do not assume carbapenem activity against MRSA—this is a critical error that can lead to treatment failure and increased mortality 1, 3
• Always verify methicillin susceptibility before relying on meropenem for staphylococcal coverage 2