What is the treatment for non-gonococcal arthritis when MRSA is not suspected?

• A. Penicillin or a cephalosporin
• B. Vancomycin
• C. Azithromycin
• D. Ciprofloxacin

Answer: (B)

Non-gonococcal septic arthritis is most commonly caused by Staphylococcus aureus, so the goal is to cover the organisms most likely to cause joint infection. If MRSA is not suspected, the antibiotic choice should target methicillin-susceptible Staph aureus and streptococci with a beta-lactam that the organism is reliably susceptible to. The preferred options are nafcillin or oxacillin, or cefazolin, which provide strong activity against MSSA and streptococci with good tissue penetration. Vancomycin, while it covers MRSA well, is not the ideal first choice when MRSA is unlikely because it is less effective against MSSA and carries risks of toxicity; it is reserved for cases where MRSA is suspected or confirmed, or when a patient cannot receive beta-lactams due to allergy. After cultures return, therapy should be narrowed to the most appropriate agent (e.g., MSSA-directed beta-lactam) to optimize efficacy and minimize toxicity.