From the Guidelines
For Methicillin-Sensitive Staphylococcus aureus (MSSA) bacteremia, the first-line intravenous antibiotic treatment is nafcillin or oxacillin, typically dosed at 2 grams every 4 hours for adults, as recommended by the most recent guidelines 1. The choice of antibiotic is crucial in managing MSSA bacteremia, and beta-lactam antibiotics such as nafcillin and oxacillin are preferred due to their effectiveness in binding to penicillin-binding proteins in the bacterial cell wall, disrupting cell wall synthesis more effectively than glycopeptides like vancomycin.
- Key considerations in treatment include:
- Dosing: 2 grams every 4 hours for adults
- Alternative: Cefazolin, administered at 2 grams every 8 hours (adjusted for renal function)
- Treatment duration: Generally 2 weeks for uncomplicated bacteremia, extending to 4-6 weeks for complicated cases involving endocarditis, osteomyelitis, or persistent bacteremia
- Monitoring: Clinical improvement, negative follow-up blood cultures, and resolution of fever, typically within 72 hours of appropriate therapy For patients with severe penicillin allergies, vancomycin can be used (15-20 mg/kg every 8-12 hours, targeting trough levels of 15-20 μg/mL), though it's less effective than beta-lactams against MSSA, as noted in guidelines from the Infectious Diseases Society of America 1.
- Additional considerations:
- Ceftriaxone (2 grams daily) may be considered for outpatient therapy after clinical improvement
- Blood cultures should be repeated every 24-48 hours until clearance is documented
- The management of MSSA bacteremia should include identification, elimination, and/or debridement of the primary source and other sites of infection when possible, as recommended by guidelines for the treatment of MRSA infections, which can also inform the treatment of MSSA infections 1.
From the FDA Drug Label
DOSAGE AND ADMINISTRATION Nafcillin for Injection, USP is available for intramuscular and intravenous use. The usual intravenous dosage for adults is 500 mg every 4 hours. For severe infections, 1 gram every 4 hours is recommended. In severe staphylococcal infections, therapy with nafcillin should be continued for at least 14 days
The recommended IV antibiotic for Methicillin-Sensitive Staphylococcus aureus (MSSA) bacteremia is nafcillin. The usual intravenous dosage for adults is 500 mg every 4 hours, and for severe infections, 1 gram every 4 hours is recommended. Therapy should be continued for at least 14 days in severe staphylococcal infections 2.
From the Research
Recommended IV Antibiotics for MSSA Bacteremia
The following IV antibiotics are recommended for the treatment of Methicillin-Sensitive Staphylococcus aureus (MSSA) bacteremia:
Key Considerations
- Initial treatment for S aureus bacteremia typically includes antibiotics active against MRSA, such as vancomycin or daptomycin, until antibiotic susceptibility results are available 3
- Once antibiotic susceptibility results are available, antibiotics should be adjusted to cefazolin or antistaphylococcal penicillins for MSSA 3
- Source control is a critical component of treating S aureus bacteremia and may include removal of infected intravascular or implanted devices, drainage of abscesses, and surgical debridement 3
- Clinical outcomes did not vary between nafcillin/oxacillin and cefazolin, suggesting that cefazolin may be a suitable alternative for patients with non-severe penicillin allergies 4, 6
Comparative Effectiveness
- Studies have shown similar clinical efficacy between cefazolin and antistaphylococcal penicillins for the treatment of MSSA bacteremia 4, 6
- Cefazolin may offer advantages over antistaphylococcal penicillins, including more convenient dosing regimens and lower rates of discontinuation due to adverse drug reactions 6