What is the best oral antibiotic for treating infectious bursitis?

Oral Antibiotic Treatment for Infectious Bursitis

For infectious bursitis, the best oral antibiotic is dicloxacillin (500 mg four times daily) or cephalexin (500 mg three times daily), as these provide optimal coverage against Staphylococcus aureus, which causes the majority of cases. 1

First-Line Oral Therapy

Dicloxacillin or cephalexin should be your default oral antibiotics for infectious bursitis in patients without MRSA risk factors. 2 These agents target methicillin-sensitive S. aureus (MSSA), which accounts for approximately 80-85% of septic bursitis cases. 3, 4

• Dicloxacillin: 500 mg orally four times daily 2
• Cephalexin: 500 mg orally three times daily 2

Both options provide excellent anti-staphylococcal activity and are recommended by the Infectious Diseases Society of America for purulent skin and soft tissue infections, which share similar microbiology with infectious bursitis. 2

MRSA Coverage When Needed

If MRSA is suspected or confirmed (healthcare exposure, injection drug use, prior MRSA infection, or high local prevalence), switch to oral agents with MRSA activity. 1

Your oral MRSA-active options include:

• Trimethoprim-sulfamethoxazole (TMP-SMX): 160-800 mg twice daily 2
• Doxycycline: 100 mg twice daily 2
• Clindamycin: 300 mg three times daily (if susceptibility confirmed) 2, 1
• Linezolid: 600 mg twice daily (reserve for severe cases or intolerance to other agents) 1

Treatment Duration

Treat for a total of 2-3 weeks, starting with IV antibiotics if the patient is hospitalized or severely ill, then transitioning to oral therapy once clinical improvement occurs. 1 The Infectious Diseases Society of America recommends this approach, with transition criteria including being afebrile for 48-72 hours and tolerating oral intake. 1

Antibiotic courses shorter than 14 days are associated with higher failure rates in both medically and surgically managed cases. 4 A French multicentre study of 272 patients demonstrated that treatment duration <14 days significantly increased failure risk (P = 0.02), even when surgical drainage was performed. 4

Special Populations Requiring Broader Coverage

For immunocompromised patients or those with open trauma to the bursa, add coverage for enteric gram-negative bacilli. 1 Consider:

• Amoxicillin-clavulanate: 875 mg twice daily 2
• Fluoroquinolones (ciprofloxacin 500-750 mg twice daily or levofloxacin 500-750 mg daily) 2

This broader approach is necessary because immunosuppressed patients may harbor atypical organisms like Pseudomonas aeruginosa, which has been documented in case reports of septic bursitis. 5

Critical Pitfalls to Avoid

Do not rely on oral antibiotics alone for initial therapy in severely ill patients with extensive cellulitis, fever, or systemic toxicity—these patients require initial IV therapy. 1, 4 A multicentre study showed IV antibiotics were preferentially used when fever (P = 0.003) or extensive cellulitis (P = 0.002) was present. 4

Never use rifampin as monotherapy or routine adjunctive therapy for bursitis—it is not recommended for skin and soft tissue infections. 1

Obtain bursal fluid cultures before starting antibiotics whenever possible to guide definitive therapy. 1 However, recognize that 19% of bursal aspirates may remain culture-negative despite clinical infection. 4

Do not stop antibiotics at 7 days even if symptoms improve—complete the full 14-21 day course to prevent recurrence. 6, 4 While one study suggested 7 days might suffice in non-immunosuppressed surgical patients, more recent evidence demonstrates higher failure rates with shorter courses. 6, 4

Algorithm for Antibiotic Selection

1. Assess MRSA risk factors (healthcare exposure, injection drug use, prior MRSA, high local prevalence) 1

   • No risk factors: Start dicloxacillin or cephalexin 2
   • MRSA risk present: Start TMP-SMX or doxycycline 2, 1

2. Evaluate for immunosuppression or open trauma 1

   • If present: Use amoxicillin-clavulanate or add gram-negative coverage 1

3. Determine severity 4

   • Mild (no fever, limited cellulitis): Oral therapy acceptable 4
   • Severe (fever, extensive cellulitis): Start IV, transition to oral after 48-72 hours afebrile 1, 4

4. Adjust based on culture results when available 1, 4

5. Treat for 14-21 days total 1, 4