What is the first-line treatment for non-gonococcal arthritis when MRSA is suspected?

• A. IV vancomycin
• B. IV ceftriaxone
• C. Oral penicillin
• D. Doxycycline

Answer: (A)

When non-gonococcal septic arthritis is suspected, the priority is to cover MRSA because it is a common and potentially devastating cause of joint infection, and delaying effective therapy can lead to joint damage. Vancomycin given IV provides reliable MRSA coverage and achieves good concentrations in the synovial fluid, making it the best first-line empiric choice while cultures are pending.

Ceftriaxone does not reliably cover MRSA, so it isn’t sufficient when MRSA is suspected. Penicillin would be ineffective against MRSA due to resistance mechanisms. Doxycycline can work against some MRSA strains, but it does not offer the consistent bactericidal activity or dependable joint penetration needed for septic arthritis, so it’s not the preferred initial therapy in this setting.

Thus, starting intravenous vancomycin promptly targets the most likely and most dangerous bacteria in this scenario.