What antibiotics are effective against Methicillin-resistant Staphylococcus aureus (MRSA) infections?

Antibiotics for MRSA Infections

Vancomycin is the first-line antibiotic for serious MRSA infections, administered at 15-20 mg/kg/dose (actual body weight) every 8-12 hours, with trough targets of 15-20 μg/mL for severe infections. 1, 2

First-Line Parenteral Options for Serious MRSA Infections

Vancomycin

• Dosing: 15-20 mg/kg/dose (actual body weight) every 8-12 hours, not to exceed 2 g per dose 1, 2
• Consider loading dose of 25-30 mg/kg for severe infections (sepsis, meningitis, pneumonia) 1, 2
• Target trough: 15-20 μg/mL for severe infections 1, 2
• Monitor trough levels before 4th or 5th dose 2
• Standard 1 g every 12 hours is inadequate for most serious infections 3

Daptomycin

• Dosing: 6-10 mg/kg IV once daily 1, 2, 4
• Only antibiotic proven non-inferior to vancomycin for MRSA bacteremia 5
• Contraindicated in pneumonia due to inactivation by pulmonary surfactant 1
• Monitor CPK levels for myopathy 2

Linezolid

• Dosing: 600 mg IV/PO twice daily 1, 2, 6
• Superior to vancomycin for MRSA pneumonia 2, 5
• Excellent CNS penetration for MRSA meningitis 1, 2
• 100% oral bioavailability allows IV-to-oral switch 6
• Monitor for thrombocytopenia with prolonged use 2

Alternative Parenteral Options

Telavancin

• Dosing: 10 mg/kg IV once daily 1
• Consider for vancomycin treatment failures 1

Quinupristin-dalfopristin

• Dosing: 7.5 mg/kg IV every 8 hours 1
• Reserved for infections with limited treatment options 1

Oral Options for Less Severe MRSA Infections

Trimethoprim-sulfamethoxazole (TMP-SMX)

• Dosing: 1-2 double-strength tablets twice daily or 4 mg/kg/dose (TMP component) twice daily 1, 2
• Often combined with rifampin 600 mg daily for osteomyelitis 1

Clindamycin

• Dosing: 300-450 mg PO three times daily or 600 mg IV/PO three times daily 1, 2
• Only if susceptibility confirmed (D-test negative) 1, 2
• Higher risk of Clostridioides difficile infection 2

Doxycycline/Minocycline

• Dosing: 100 mg PO twice daily 1, 2
• Good option for uncomplicated skin infections 2

Treatment by Infection Type

MRSA Bacteremia/Endocarditis

• Vancomycin IV for 2-6 weeks depending on source 1
• Daptomycin 6-10 mg/kg IV daily is an excellent alternative 1, 4
• Consider adding rifampin 600 mg daily for prosthetic valve endocarditis 1

MRSA Pneumonia

• Vancomycin IV or linezolid 600 mg IV/PO twice daily for 7-21 days 1
• Linezolid may be superior for hospital-acquired pneumonia 5
• Do not use daptomycin for pneumonia 1

MRSA Osteomyelitis

• Surgical debridement plus antibiotics for at least 8 weeks 1
• Options include:
  • Vancomycin IV 1
  • Daptomycin 6 mg/kg IV daily 1
  • TMP-SMX plus rifampin 1
  • Linezolid 600 mg twice daily 1

MRSA CNS Infections

• Vancomycin IV for 4-6 weeks 1
• Consider adding rifampin 600 mg daily 1
• Alternatives: linezolid 600 mg twice daily or TMP-SMX 5 mg/kg IV every 8-12 hours 1

Uncomplicated MRSA Skin Infections

• Incision and drainage is primary treatment 1, 2
• Oral options: TMP-SMX, doxycycline, clindamycin (if susceptible), or linezolid 1, 2

Special Considerations

• For vancomycin MIC ≥2 μg/mL, consider alternative agents 1
• For persistent MRSA bacteremia despite adequate vancomycin therapy:
  • Search for and remove other foci of infection 1
  • Consider high-dose daptomycin (10 mg/kg/day) in combination with another agent 1
• Pediatric dosing: vancomycin 15 mg/kg/dose IV every 6 hours for serious infections 1

Common Pitfalls to Avoid

1. Underdosing vancomycin (1g q12h) for serious infections 3
2. Failing to monitor vancomycin trough levels in high-risk patients 2
3. Using daptomycin for pneumonia 1, 2
4. Not performing source control (drainage of abscesses) 1, 2
5. Continuing vancomycin despite poor clinical response when MIC ≥2 μg/mL 1
6. Using clindamycin without confirming susceptibility (D-test) 1, 2

By following these evidence-based recommendations for MRSA treatment, clinicians can optimize outcomes while minimizing the risk of treatment failure and antibiotic resistance.