What antibiotics are recommended for septic arthritis of the knee?

Antibiotic Treatment for Septic Arthritis of the Knee

Initiate IV vancomycin 30 mg/kg/day in 2 divided doses (or 15 mg/kg every 6 hours) immediately after obtaining synovial fluid cultures to cover MRSA, which has become a major cause of septic arthritis in the United States. 1, 2

Empiric Antibiotic Selection

First-Line Therapy for Adults

• Vancomycin is the drug of choice for empiric coverage given the high prevalence of MRSA in septic arthritis 1, 2, 3
• Dosing: 30-60 mg/kg/day IV in 2-4 divided doses, or 15 mg/kg IV every 6 hours 1
• Start immediately after joint aspiration is obtained, do not wait for culture results 2

Alternative Empiric Options for Adults

If MRSA is less likely based on local epidemiology or patient risk factors:

• Linezolid 600 mg IV/PO every 12 hours 1
• Daptomycin 6 mg/kg IV daily 1
• Teicoplanin 6-12 mg/kg IV every 12 hours for 3 doses, then daily 1

Pediatric Empiric Therapy

• Vancomycin 15 mg/kg/dose IV every 6 hours (40 mg/kg/day in 4 divided doses) 1
• Clindamycin 10-13 mg/kg/dose IV every 6-8 hours as alternative if local clindamycin resistance is low 2
• Consider Kingella kingae in children <4 years old 2

Definitive Antibiotic Therapy (Culture-Directed)

Methicillin-Susceptible Staphylococcus aureus (MSSA)

Switch from vancomycin to:

• Nafcillin or oxacillin 1-2 g IV every 4 hours 1, 2
• Cefazolin 1 g IV every 8 hours (more convenient, less bone marrow suppression) 1
• Clindamycin 600 mg IV every 8 hours (if penicillin allergic) 1

Methicillin-Resistant Staphylococcus aureus (MRSA)

Continue vancomycin as primary therapy 1, 2

• Consider adding rifampin 600 mg PO daily or 300-450 mg PO twice daily for enhanced bone and biofilm penetration 1, 2
• Rifampin should never be used as monotherapy 1

Streptococcal Infections

• Penicillin G 20-24 million units IV daily continuous infusion or divided doses 1
• Ceftriaxone 1-2 g IV every 24 hours 1

Polymicrobial Infections

• Dual antibiotic coverage is mandatory when multiple organisms are identified 2
• Example: Linezolid for MRSA plus ciprofloxacin for Pseudomonas aeruginosa 2

Treatment Duration

Native Joint Septic Arthritis

• 3-4 weeks total duration for uncomplicated bacterial arthritis 1, 2, 3
• Recent evidence suggests 2 weeks may be adequate after surgical drainage in select cases (predominantly small joints) 1
• Extend to 6 weeks if imaging shows concomitant osteomyelitis, which occurs in up to 30% of pediatric cases 2, 3

Prosthetic Joint Infections

• 12 weeks is superior to 6 weeks for prosthetic joint infections treated with debridement and implant retention 1
• For hip prostheses with one-stage or two-stage exchange: 3 months total 1
• For knee prostheses with one-stage or two-stage exchange: 6 months total 1

Pediatric Considerations

• 10 days total may suffice for previously healthy children in Western settings with appropriate surgical drainage 4
• Neonates, immunocompromised patients, or MRSA cases may require longer courses 4

Route of Administration

IV to Oral Transition

• Oral antibiotics are not inferior to IV therapy for most cases of septic arthritis 5
• Switch to oral after 2-4 days if patient is clinically improving, afebrile, and can tolerate oral intake 4
• Use high doses of well-absorbing antibiotics with 4-times-daily administration for time-dependent antibiotics 4

Oral Options for MRSA (after initial IV therapy)

• Linezolid 600 mg PO every 12 hours 1
• TMP-SMX (trimethoprim 4 mg/kg/dose) PO every 8-12 hours plus rifampin 600 mg PO daily 1
• Fusidic acid 500 mg PO every 8 hours or 750 mg every 12 hours plus rifampin 1

Critical Pitfalls and Caveats

Surgical Management is Mandatory

• Antibiotic therapy alone is insufficient—immediate joint drainage via arthrocentesis, arthroscopy, or open debridement is required 2, 3, 6
• Surgical emergencies require immediate debridement with intraoperative cultures rather than waiting for aspiration results 2

MRSA Coverage

• Do not delay MRSA coverage while awaiting cultures—MRSA is associated with worse outcomes 3, 6
• Vancomycin remains the primary treatment despite concerns about bone penetration 2

Monitoring and Adjustments

• Follow CRP and ESR to monitor treatment response 2
• Monitor for vancomycin toxicity and adjust dosing based on trough levels 1
• Be vigilant for drug interactions and adverse effects, especially in elderly patients 2

Special Populations

• Sickle cell disease: Consider Salmonella species as causative organism 2
• Gonococcal arthritis: Requires different treatment approach (ceftriaxone-based regimen) 5
• Negative cultures: Do not rule out infection—consider percutaneous bone biopsy if clinical suspicion remains high 2

Adjunctive Therapy

• Early NSAID administration in conjunction with antibiotics may decrease articular cartilage damage 7
• Avoid intra-articular corticosteroids during active infection 2