Antibiotic Treatment for Septic Prepatellar Bursitis Caused by Staphylococcus aureus
For an otherwise healthy adult with septic prepatellar bursitis caused by Staphylococcus aureus, initial empirical therapy should cover MRSA with vancomycin IV or oral clindamycin/TMP-SMX, then de-escalate to cefazolin or an antistaphylococcal penicillin once MSSA susceptibility is confirmed. 1, 2
Initial Management Approach
Drainage is essential - incision and drainage of the bursa is the primary treatment, with antibiotics serving as adjunctive therapy. 2 Cultures of the bursal fluid must be obtained during drainage to guide targeted antibiotic therapy. 2
Systemic antibiotics are indicated when any of the following are present: 2
- Temperature >38°C or <36°C
- Tachypnea >24 breaths/minute
- Tachycardia >90 beats/minute
- WBC >12,000 or <400 cells/μL
- Erythema and induration extending >5 cm from the wound edge
Empirical Antibiotic Selection (Before Culture Results)
Since Staphylococcus aureus (particularly penicillin-resistant strains) is the most common pathogen in septic bursitis, empirical coverage should target both MSSA and MRSA until susceptibilities are known. 3
For outpatients who are not acutely ill: 1, 4
- Clindamycin 600 mg PO three times daily (covers both MSSA and CA-MRSA) 1
- TMP-SMX (covers CA-MRSA but add amoxicillin if streptococcal coverage desired) 1
- Doxycycline or minocycline (covers CA-MRSA but add a β-lactam if streptococcal coverage desired) 1
For hospitalized or acutely ill patients: 1, 4
- Vancomycin 15 mg/kg IV every 12 hours (adjust to trough 10-20 μg/mL) 1, 2
- Linezolid 600 mg IV or PO twice daily 1
- Daptomycin 4 mg/kg IV once daily 1
Definitive Therapy (After Susceptibility Results)
For Methicillin-Susceptible S. aureus (MSSA):
Switch to β-lactam antibiotics immediately once MSSA is confirmed, as they are superior to vancomycin for MSSA infections. 1, 5, 6
- Cefazolin 1 g IV every 8 hours (for moderate to severe infections) 2
- Cephalexin 500 mg PO four times daily (for mild infections transitioning to oral therapy) 2
- Nafcillin or oxacillin (alternative antistaphylococcal penicillins) 1, 5
For penicillin-allergic patients (non-anaphylactic reactions): 1, 5
- First-generation cephalosporins like cefazolin are reasonable 1
- Avoid cephalosporins in patients with immediate-type hypersensitivity (urticaria, angioedema, bronchospasm, anaphylaxis) 5
For true penicillin allergy with anaphylaxis: 1, 5
For Methicillin-Resistant S. aureus (MRSA):
Continue MRSA-active therapy: 1, 5, 7
- Vancomycin IV (most common for severe infections) 1, 7
- Linezolid 600 mg PO/IV twice daily 1
- Daptomycin 4 mg/kg IV once daily 1
- Clindamycin 600 mg PO/IV three times daily (if local resistance rates <10%) 1
Duration of Therapy
5-7 days of antibiotics after adequate drainage for most uncomplicated cases. 2 Treatment should be extended if the infection has not improved within this timeframe. 2 The duration should be proportional to how long the infection was present before treatment initiation. 3
Monitoring and Follow-up
Reassess within 48-72 hours to ensure clinical improvement. 2 If symptoms worsen or fail to improve despite appropriate antibiotics and drainage, consider: 2
- Inadequate source control (incomplete drainage)
- Resistant organism
- Alternative diagnosis
- Metastatic infection
Critical Pitfalls to Avoid
Do not treat with antibiotics alone without drainage - this is the most common error and leads to treatment failure. 2
Do not fail to obtain cultures before starting antibiotics - culture data is essential for targeted therapy. 2
Do not continue vancomycin for MSSA - β-lactams are superior and should be used once susceptibility is confirmed. 1, 6
Do not assume all S. aureus is MRSA - in many community settings, MSSA remains common, and empirical MRSA coverage can be narrowed based on local epidemiology and culture results. 1, 5
Consider MRSA risk factors: prior MRSA infection, recent hospitalization, injection drug use, or residence in areas with high CA-MRSA prevalence. 1