Antibiotics for MRSA Treatment
Vancomycin 15-20 mg/kg IV every 8-12 hours (not to exceed 2 g per dose) is the first-line treatment for serious MRSA infections, with linezolid 600 mg IV/PO twice daily as an equally effective alternative, particularly for pneumonia. 1
First-Line Antibiotic Options by Infection Type
Serious/Invasive MRSA Infections (Bacteremia, Endocarditis, Pneumonia, Osteomyelitis, Meningitis)
Parenteral Options:
- Vancomycin 15-20 mg/kg IV every 8-12 hours (actual body weight, max 2 g/dose) targeting trough levels of 15-20 μg/mL for serious infections 1
- Loading dose of 25-30 mg/kg may be considered in critically ill patients with sepsis, meningitis, pneumonia, or endocarditis (infuse over 2 hours with antihistamine premedication to prevent red man syndrome) 1
- Linezolid 600 mg IV/PO every 12 hours—particularly advantageous for MRSA pneumonia where it may be superior to vancomycin, and in patients with renal dysfunction or fluctuating renal function 1, 2
- Daptomycin 6 mg/kg IV daily for bacteremia/endocarditis; use 10 mg/kg/day for reduced vancomycin susceptibility (MIC >1 μg/mL), combined with another agent 1, 3
Critical Caveat: Daptomycin is contraindicated for pneumonia due to inactivation by pulmonary surfactant—never use it for respiratory tract infections 3
Skin and Soft Tissue Infections (SSTI)
Oral Options (Uncomplicated):
- Trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets (160-320/800-1600 mg) PO twice daily—first-line oral agent with bactericidal activity 4, 5
- Doxycycline 100 mg PO twice daily—equally effective as TMP-SMX 5
- Clindamycin 300-450 mg PO three times daily—provides dual MRSA and streptococcal coverage but only use if local MRSA resistance <10% due to inducible resistance concerns 5
Parenteral Options (Complicated/Severe):
- Vancomycin 1 g IV every 12 hours for patients with normal renal function and non-obese (trough monitoring not required for uncomplicated SSTI) 1
- Linezolid 600 mg IV/PO every 12 hours 1
Essential: Incision and drainage is the mainstay of therapy and must be performed before or concurrent with antibiotics for any abscess or purulent wound 5
Urinary Tract Infections
Only treat symptomatic MRSA UTI—do not treat asymptomatic bacteriuria as it represents colonization and promotes resistance 4
Treatment Options:
- TMP-SMX 1-2 double-strength tablets PO twice daily (preferred first-line oral agent) 4
- Vancomycin IV for severe/complicated infections 4
- Linezolid 600 mg PO/IV twice daily (alternative) 4
Vancomycin Dosing and Monitoring Algorithm
Standard Dosing
- Adults: 15-20 mg/kg IV every 8-12 hours based on actual body weight, not to exceed 2 g per dose 1
- Pediatrics: 15 mg/kg/dose IV every 6 hours for serious infections 1, 6
When to Monitor Trough Levels
Mandatory monitoring: 1
- Serious infections (bacteremia, endocarditis, osteomyelitis, meningitis, pneumonia, necrotizing fasciitis)
- Morbidly obese patients
- Renal dysfunction or dialysis patients
- Fluctuating volumes of distribution
No monitoring needed: Uncomplicated SSTI in patients with normal renal function who are not obese receiving 1 g every 12 hours 1
Target Trough Concentrations
- 15-20 μg/mL for serious infections (bacteremia, endocarditis, osteomyelitis, meningitis, pneumonia, severe SSTI) 1, 7
- Obtain trough before 4th or 5th dose at steady state 1
- Peak monitoring is not recommended 1
Dosing in Critically Ill Trauma Patients
Standard 1 g every 12 hours is inadequate—doses of at least 1 g every 8 hours are needed to achieve therapeutic troughs of 15-20 μg/mL 8
Treatment Duration
- Uncomplicated SSTI: 5-10 days 5
- Complicated SSTI: 7-14 days 5
- Respiratory tract infections (tracheitis/pneumonia): 7-21 days depending on severity; 7-10 days for uncomplicated, 14-21 days for complicated or slow response 6
- Bacteremia/Endocarditis: Up to 42 days depending on source control and clinical response 3
Alternative Agents for Specific Scenarios
When Vancomycin Fails or MIC >2 μg/mL
Use alternative agents—vancomycin is inadequate for VISA/VRSA (MIC >2 μg/mL): 1
- High-dose daptomycin 10 mg/kg/day combined with gentamicin 1 mg/kg every 8 hours, rifampin 600 mg daily, linezolid 600 mg twice daily, TMP-SMX 5 mg/kg twice daily, or a beta-lactam 1
- Quinupristin-dalfopristin 7.5 mg/kg IV every 8 hours 1
Renal Dysfunction or Nephrotoxicity Risk
Linezolid is preferred in patients with renal insufficiency, fluctuating renal function, or receiving concurrent nephrotoxic agents (aminoglycosides), as vancomycin dosing is difficult and underdosing is common 1
Dual Coverage for MRSA + Streptococci
- Clindamycin alone if local MRSA resistance <10% 5
- TMP-SMX or doxycycline + beta-lactam (cephalexin 500 mg four times daily or amoxicillin) 5
Critical Pitfalls to Avoid
- Never use beta-lactam antibiotics alone for MRSA—they have zero activity against methicillin-resistant organisms 5
- Never use daptomycin for pneumonia—it is inactivated by pulmonary surfactant 3
- Never use rifampin as monotherapy—rapid resistance develops; only use in combination 1, 4
- Do not underdose vancomycin in obese patients—use actual body weight for dosing calculations 1
- Do not use traditional 1 g every 12 hours vancomycin in critically ill trauma patients—at least 1 g every 8 hours is required 8
- Do not treat asymptomatic MRSA bacteriuria—it promotes resistance without clinical benefit 4
- Do not use clindamycin if local MRSA resistance >10% or inducible resistance is detected 5
- Do not continue vancomycin for isolates with MIC >2 μg/mL—switch to alternative agents 1
- Do not skip surgical debridement—failure to remove infected foci is associated with treatment failure and higher mortality 1, 5
Pediatric Considerations
- Vancomycin 15 mg/kg/dose IV every 6 hours for serious infections 1, 6
- Linezolid: 600 mg twice daily for children >12 years; 10 mg/kg/dose every 8 hours for children <12 years 4
- Clindamycin 10-13 mg/kg/dose IV every 6-8 hours if stable without bacteremia and local resistance <10% 6
- Avoid tetracyclines (doxycycline) in children <8 years 4