Antibacterial Activity of Synovial Fluid During Therapy of Septic Arthritis

Therapeutic concentrations of antimicrobial agents in infected joints during systemic therapy were demonstrated in 29 patients by measuring synovial fluid antibacterial activity. Antimicrobial agents used were penicillin G, phenoxymethyl penicillin, nafcillin, cephaloridine, tetracycline, erythromycin and lincomycin. Passage of antibiotic into synovial fluid was evaluated in simultaneously collected serum and synovial fluid specimens by two methods: a) a tube‐dilution procedure for antibacterial liter of the two fluids against the microorganism recovered from the joint or a suitable laboratory species and b) a bioassay test of antibiotic concentration. In general, the bioassay results closely supported the information obtained by tube‐dilution antibacterial activity determination. Demonstration that effective concentrations of an antibiotic are present in an infected joint during systemic therapy obviates the need for local instillation of drug into the synovial space. Since passage of antimicrobial agents into synovial fluid during systemic therapy can be reliably established by the more simple tube‐dilution method, every patient with septic arthritis should be monitored by such determinations during the course of therapy.