In a healthy adult with septic bursitis (marked increase in synoviocytes), no drug allergies and no risk factors for methicillin‑resistant Staphylococcus aureus, what is the appropriate first‑line oral antibiotic regimen?

Antibiotic Selection for Septic Bursitis with High Synoviocyte Count

In a healthy adult with septic bursitis and no MRSA risk factors, oral dicloxacillin 500 mg every 6 hours or cephalexin 500 mg every 6 hours for 5–7 days is the appropriate first-line regimen after drainage, targeting methicillin-susceptible Staphylococcus aureus which causes >80% of cases.

Primary Treatment Principle

• Drainage (aspiration or surgical) is the cornerstone of septic bursitis management and must be performed before or concurrent with antibiotic therapy. 1, 2
• Antibiotics function as adjuncts to adequate source control; without drainage, antibiotic therapy alone frequently fails. 2, 3

Pathogen Profile and Antibiotic Selection

Microbiology

• Staphylococcus aureus accounts for >80% of septic bursitis cases, with the majority being methicillin-susceptible strains in patients without MRSA risk factors. 4, 5
• The marked increase in synoviocytes confirms an infectious rather than inflammatory process, supporting empiric anti-staphylococcal coverage. 6

First-Line Oral Regimens (No MRSA Risk Factors)

• Dicloxacillin 500 mg orally every 6 hours provides excellent MSSA coverage and is a preferred oral anti-staphylococcal agent. 1
• Cephalexin 500 mg orally every 6 hours is an equally effective alternative first-generation cephalosporin. 1
• Both agents achieve high cure rates when combined with adequate drainage in immunocompetent patients. 1, 3

Treatment Duration

• A 5-day antibiotic course is appropriate for uncomplicated septic bursitis when clinical improvement occurs; extend only if symptoms persist. 1, 3
• Serial aspirations demonstrating culture sterility within 4 days predict successful outcomes when antibiotics are continued for 5 additional days after documented sterility. 3
• Patients treated within 2 weeks of symptom onset achieve bursal fluid sterility within 1 week of therapy. 3

When to Escalate or Modify Therapy

Indications for Hospitalization and IV Antibiotics

• Admit patients with fulminant local infection, systemic toxicity (fever, tachycardia, hypotension), or immunocompromise for intravenous therapy. 4, 7
• Cefazolin 1–2 g IV every 8 hours is the preferred IV agent for hospitalized patients with MSSA septic bursitis. 2

Surgical Intervention

• Surgical drainage or bursectomy is indicated when patients fail to respond to IV antibiotics plus percutaneous aspiration. 4, 7
• Endoscopic bursectomy may decrease morbidity compared to open procedures in refractory cases. 5

Complex Presentations Requiring Extended Therapy

• When septic bursitis is complicated by bacteremia, endocarditis, or osteomyelitis, extend antibiotic duration to 4–6 weeks following disease-specific guidelines. 2

MRSA Coverage (When Risk Factors Present)

Although this patient has no MRSA risk factors, coverage would be indicated if any of the following were present:

• Clindamycin 300–450 mg orally every 6 hours covers both MSSA and MRSA when local clindamycin resistance is <10%. 1
• Trimethoprim-sulfamethoxazole 1–2 double-strength tablets twice daily provides MRSA coverage but must be combined with a beta-lactam for streptococcal activity. 1
• Vancomycin 15–20 mg/kg IV every 8–12 hours is first-line for hospitalized patients requiring MRSA coverage. 1

Critical Management Algorithm

1. Perform bursal aspiration immediately – send fluid for Gram stain, culture, cell count with differential, crystal analysis, and glucose. 7
2. Initiate oral dicloxacillin or cephalexin targeting MSSA in patients without MRSA risk factors. 1
3. Reassess within 24–48 hours – treatment failure rates of ~21% mandate early follow-up. 1
4. Perform serial aspirations every 2–3 days until cultures are sterile, then continue antibiotics for 5 additional days. 3
5. Escalate to IV therapy or surgery if no improvement after 48–72 hours of appropriate oral antibiotics. 4, 7

Common Pitfalls to Avoid

• Do not treat septic bursitis with antibiotics alone without drainage; this approach has high failure rates. 2, 3
• Do not add routine MRSA coverage in healthy adults without risk factors (penetrating trauma, injection drug use, known MRSA colonization, prior MRSA infection, or systemic inflammatory response). 1
• Do not use intrabursal corticosteroid injections when infection is suspected, as this worsens septic bursitis. 4, 7
• Do not delay surgical consultation when patients fail to respond to antibiotics plus aspiration after 48–72 hours. 4, 5

Adjunctive Measures

• Elevate the affected limb to promote drainage and reduce swelling. 1
• Address underlying causes such as chronic microtrauma (e.g., occupational kneeling) to prevent recurrence. 7
• Conservative management with ice, rest, and analgesics complements antibiotic therapy in the acute phase. 7