What is the recommended antibiotic treatment and duration of therapy for a patient with extensor tenosynovitis due to Methicillin-Sensitive Staphylococcus aureus (MSSA) infection?

Treatment of MSSA Extensor Tenosynovitis

For MSSA extensor tenosynovitis, initiate cefazolin 1-2 grams IV every 8 hours or nafcillin/oxacillin 2 grams IV every 4-6 hours after urgent surgical drainage, transition to oral dicloxacillin 500 mg four times daily once clinically improved, and complete a total duration of 2-3 weeks of antibiotics. 1

Immediate Surgical Management

Early surgical drainage is mandatory and must be performed urgently, as inadequate drainage is the most common cause of treatment failure regardless of antibiotic choice. 1 This is the single most critical intervention that determines outcome—antibiotics alone will fail without adequate source control. 1

• Obtain cultures of blood and abscess material before initiating antibiotics to confirm MSSA and guide definitive therapy. 1
• Clinical improvement should be evident within 48-72 hours; lack of improvement warrants repeat imaging to assess for inadequate drainage. 1

Initial Intravenous Antibiotic Therapy

Both cefazolin and nafcillin/oxacillin have equivalent efficacy for MSSA soft tissue infections with abscess formation. 1 The choice between these agents can be based on practical considerations:

• Cefazolin 1-2 grams IV every 8 hours is preferred by many clinicians due to less frequent dosing and lower toxicity rates. 1, 2
• Nafcillin or oxacillin 2 grams IV every 4-6 hours is equally effective but requires more frequent administration. 1
• Oxacillin is discontinued due to toxicity more frequently than cefazolin (18% vs 4%). 2

Do not add gentamicin to beta-lactam therapy—it increases nephrotoxicity without improving clinical outcomes. 3, 4

Transition to Oral Therapy

Once the patient demonstrates clinical improvement (typically within 48-72 hours), transition to oral antibiotics:

• Dicloxacillin 500 mg orally four times daily is the preferred oral agent due to best bioavailability among oral antistaphylococcal penicillins. 1, 5
• Cephalexin 500 mg orally every 6 hours is an acceptable alternative for patients with non-anaphylactic penicillin intolerance. 1, 5

Duration of Therapy

The total duration of antibiotics should be 2-3 weeks, with IV therapy initially followed by oral therapy after clinical improvement. 1 This duration applies specifically to soft tissue infections with small abscess after adequate surgical drainage. 1

• If blood cultures were positive, repeat cultures 2-4 days after starting appropriate antibiotics to document clearance. 1, 3
• Positive blood cultures beyond 72 hours would classify this as complicated bacteremia requiring 4-6 weeks of therapy. 3

Critical Pitfalls to Avoid

• Never rely on antibiotics alone without surgical drainage—this is the most common cause of treatment failure. 1
• Do not use vancomycin for MSSA if beta-lactams can be tolerated, as outcomes are inferior with vancomycin. 4
• Avoid adding aminoglycosides to beta-lactam therapy as this increases toxicity without benefit. 3, 4
• Do not use third-generation cephalosporins (ceftriaxone, cefotaxime) as first-line therapy for serious MSSA infections, as they may be associated with higher mortality compared to antistaphylococcal penicillins or cefazolin. 6

Monitoring Strategy

• Assess for clinical improvement within 48-72 hours (decreased pain, erythema, swelling, fever resolution). 1
• If no improvement occurs, obtain repeat imaging to evaluate for inadequate drainage or undrained fluid collections. 1
• For patients with positive blood cultures, document clearance with repeat cultures 2-4 days after initiating therapy. 1, 3