In septic arthritis, empiric therapy should cover MRSA with vancomycin; what additional coverage is typically used for Gram-negative organisms?

• A. Ceftriaxone
• B. Vancomycin
• C. Linezolid
• D. Doxycycline

Answer: (A)

In septic arthritis, starting therapy that covers both MRSA and common Gram-negative bacteria is essential because the infection can be caused by a mix of organisms. Vancomycin is chosen to reliably cover MRSA. To address Gram-negative pathogens, a third-generation cephalosporin such as ceftriaxone is typically added. Ceftriaxone has good activity against many Gram-negative organisms that cause joint infections (like E. coli, Klebsiella, and Proteus) and penetrates joint tissue well, making it a common partner to vancomycin in empiric regimens.

The other options don’t fit as well for broad Gram-negative coverage. Vancomycin targets MRSA but lacks Gram-negative activity. Linezolid covers MRSA but similarly doesn’t provide reliable Gram-negative coverage. Doxycycline has limited reliability for septic arthritis and isn’t a standard choice for broad Gram-negative coverage in this setting. Ceftriaxone, by contrast, effectively broadens coverage to include typical Gram-negative pathogens encountered in septic arthritis, which is why it’s the best answer.