What is the treatment for Methicillin-Sensitive Staphylococcus aureus (MSSA) infections in neonates?

From the Guidelines

For treating methicillin-sensitive Staphylococcus aureus (MSSA) infections in neonates, intravenous nafcillin or oxacillin is the first-line therapy, typically administered at 25-50 mg/kg/dose every 6-8 hours depending on the neonate's age and severity of infection. This recommendation is based on the most recent and highest quality study available, which suggests that a semisynthetic, β-lactamase–resistant penicillin (nafcillin or oxacillin) given intravenously for a minimum of 4 to 6 weeks is the standard of care for methicillin-susceptible S aureus endocarditis involving a native valve or other native cardiac tissue 1.

Key Considerations

• For less severe infections or step-down therapy, cefazolin (25-50 mg/kg/dose every 8-12 hours) may be used as an alternative 1.
• Treatment duration typically ranges from 7-14 days for uncomplicated infections to 4-6 weeks for more severe conditions like osteomyelitis, endocarditis, or meningitis.
• For neonates with penicillin allergies, clindamycin (5-7.5 mg/kg/dose every 8 hours) or vancomycin (10-15 mg/kg/dose every 6-12 hours) can be used as alternatives 1.
• The addition of gentamicin for the first 3 to 5 days may be considered to accelerate the killing of the staphylococci, but this concept is based on extrapolation from experimental models and may increase the likelihood of renal and otic toxicity 1.

Supportive Care

• Therapeutic drug monitoring is essential for vancomycin to maintain trough levels between 10-15 μg/mL for most infections.
• Supportive care including adequate hydration, temperature regulation, and respiratory support may be necessary.
• Drainage of abscesses or removal of infected catheters or devices is often required for complete resolution.
• MSSA responds well to beta-lactam antibiotics because these organisms have not developed resistance mechanisms that alter penicillin-binding proteins, unlike their methicillin-resistant counterparts.

From the FDA Drug Label

DOSAGE AND ADMINISTRATION Nafcillin for Injection, USP is available for intramuscular and intravenous use. ... Neonates 10 mg/kg IM twice daily Bacteriologic studies to determine the causative organisms and their susceptibility to nafcillin should always be performed. In severe staphylococcal infections, therapy with nafcillin should be continued for at least 14 days

The treatment for Methicillin-Sensitive Staphylococcus aureus (MSSA) infections in neonates is:

• Nafcillin administered at a dose of 10 mg/kg IM twice daily 2
• The duration of therapy should be determined by the clinical and bacteriological response of the patient, but should be continued for at least 14 days in severe staphylococcal infections.

From the Research

Treatment for Methicillin-Sensitive Staphylococcus aureus (MSSA) Infections in Neonates

• The treatment for MSSA infections in neonates involves the use of antibiotics, with options including oxacillin, cefazolin, and clindamycin 3, 4, 5, 6.
• A study published in 2023 reported the successful treatment of a premature neonate with persistent MSSA bacteremia using a combination of oxacillin and ertapenem 3.
• Another study from 1982 compared the use of clindamycin and nafcillin/methicillin in the treatment of Staphylococcus aureus osteomyelitis in children, and found that clindamycin was an effective alternative to nafcillin/methicillin 4.
• The choice of antibiotic may depend on various factors, including the severity of the infection, the patient's age and weight, and the presence of any underlying medical conditions.
• Studies have shown that cefazolin and antistaphylococcal penicillins (such as oxacillin) are effective treatments for MSSA bacteremia, with no significant difference in outcomes between the two 5, 6.
• However, it is essential to note that the treatment of MSSA infections in neonates should be guided by the results of susceptibility testing and the clinical judgment of a healthcare professional.

Antibiotic Options

• Oxacillin: a penicillinase-resistant penicillin that is effective against MSSA 3, 5.
• Cefazolin: a first-generation cephalosporin that is effective against MSSA 5, 6.
• Clindamycin: a lincosamide antibiotic that is effective against MSSA 4.
• Ertapenem: a carbapenem antibiotic that has been used in combination with oxacillin to treat persistent MSSA bacteremia in a neonate 3.
• Nafcillin/methicillin: penicillinase-resistant penicillins that are effective against MSSA 4.

Treatment Duration

• The duration of treatment for MSSA infections in neonates will depend on the severity of the infection and the patient's response to therapy.
• Studies have reported treatment durations ranging from several days to several weeks 3, 4, 5, 6.
• The treatment should be guided by the results of susceptibility testing and the clinical judgment of a healthcare professional.