What are the recommendations for antibiotic therapy and follow-up imaging in a patient post-craniotomy for glioblastoma multiforme (GBM) resection, now post-operative washout, with intra-operative cultures growing methicillin-susceptible Staphylococcus aureus (MSSA)?

From the Guidelines

For a patient with a surgical site infection after craniotomy for GBM resection with MSSA-positive cultures, I recommend a 4-6 week course of intravenous nafcillin or oxacillin at 2g every 4 hours (or cefazolin 2g every 8 hours if beta-lactam allergies are not severe). This extended duration is necessary because the infection involves bone (cranial plating) and has caused a dural defect with CSF drainage, classifying it as a complex surgical site infection with potential for meningitis or cerebritis 1. The patient should receive the first 2 weeks of antibiotics in the hospital to monitor neurological status and ensure infection control, followed by outpatient parenteral antibiotic therapy (OPAT) if clinically improving.

Key Considerations

• The choice of antibiotic is crucial, and nafcillin or oxacillin are preferred over vancomycin for MSSA infections 1.
• The duration of therapy is also critical, and a minimum of 4-6 weeks is recommended for complex surgical site infections 1.
• Follow-up imaging with contrast-enhanced MRI should be performed at 2 weeks to assess initial response and again at completion of therapy (4-6 weeks) to confirm resolution. Additional imaging may be needed if symptoms worsen.
• The patient will need neurosurgical follow-up to address the dural defect and determine if reconstruction is necessary once the infection is controlled.
• Serum inflammatory markers (CRP, ESR) should be monitored weekly to track treatment response.

Rationale

This aggressive approach is warranted because CNS infections with hardware involvement carry significant morbidity and mortality risks if inadequately treated. The use of nafcillin or oxacillin is supported by the American Heart Association guidelines for the treatment of infective endocarditis caused by MSSA 1. The duration of therapy is also supported by these guidelines, which recommend at least 6 weeks of therapy for complicated left-sided infective endocarditis caused by MSSA 1. The use of cefazolin as an alternative is supported by the Anaesthesia guidelines for antibioprophylaxis in surgery and interventional medicine 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 antibiotic therapy is Nafcillin at a dose of 1 gram every 4 hours for at least 14 days due to the presence of MSSA in intra-op cultures and the severity of the infection 2. There is no information in the provided drug labels regarding the timing and need for follow-up imaging. The choice of duration of antibiotic therapy is based on the type and severity of the infection, as well as the overall condition of the patient. Key points to consider:

• Severe staphylococcal infections require prolonged therapy
• MSSA is susceptible to Nafcillin
• Duration of therapy should be determined by the clinical and bacteriological response of the patient 2

From the Research

Antibiotic Therapy

• The patient has a large volume of purulent material in the subgaleal fluid collection, erosion of muscle, galea, and soft tissue, and removal of cranial plating with a noted dural defect and CSF drainage, with all intra-op cultures growing Methicillin-Sensitive Staphylococcus aureus (MSSA) 3, 4, 5, 6, 7.
• Based on the studies, cefazolin is a preferred antibiotic for the treatment of MSSA infections, including those complicated by bacteremia 5, 7.
• Cefazolin has been shown to have a lower risk of mortality and similar odds of recurrent infections compared to nafcillin or oxacillin for MSSA infections complicated by bacteremia 7.
• The duration of antibiotic therapy is not explicitly stated in the provided studies, but it is generally recommended to continue antibiotic therapy for at least 4-6 weeks for complicated infections such as those involving bone or joint infections, or for infections with a high risk of complications 3, 4, 6.

Follow-up Imaging

• There is no direct evidence in the provided studies regarding the timing and need for follow-up imaging in a patient with a history of craniotomy for GBM resection and subsequent washout.
• However, it is generally recommended to follow up with imaging studies, such as MRI or CT scans, to monitor for any signs of infection, abscess, or other complications, especially in patients with a history of neurosurgical procedures 3, 4, 6.
• The frequency and timing of follow-up imaging should be determined on a case-by-case basis, taking into account the patient's clinical condition, the severity of the infection, and the presence of any underlying medical conditions.

Choice and Duration of Antibiotic Therapy

• Based on the studies, a recommended choice of antibiotic therapy for this patient would be cefazolin, given its effectiveness in treating MSSA infections and its relatively low risk of adverse reactions 5, 7.
• The duration of antibiotic therapy should be individualized based on the patient's clinical response, the severity of the infection, and the presence of any underlying medical conditions. A minimum duration of 4-6 weeks is generally recommended for complicated infections.