Treatment of Septic Arthritis with Penicillin or Cephalosporin Allergy When Gram-Negative Rods Are Found on Synovial Fluid Gram Stain

This protocol addresses septic arthritis in a patient with a history of penicillin or cephalosporin allergy in whom the synovial fluid Gram stain reveals gram-negative rods. The Gram stain result directly informs antibiotic selection, and the documented allergy eliminates standard beta-lactam options, narrowing the available treatment choices considerably.

Antibiotic treatment should be based on the results of the synovial fluid Gram stain. With gram-negative rods identified and a beta-lactam allergy present, intravenous antibiotic therapy is directed toward agents outside the penicillin and cephalosporin classes. The specific choice and the expected duration of treatment — which varies by joint size — are detailed in the full protocol.