Antibiotic penetration of synovial fluid in infected and normal knee joints

A spectrum of new and commonly used antibiotics was examined with regard to their ability to penetrate into joint fluid in normal and E. coli infected rabbit knee joints. In order to carry out this investigation a new, simple method of measuring antibiotics in very small amounts of synovial fluid was developed. Cephalothin, cefazolin, cefoxitin, carbenicillin, amikacin, and gentamicin all penetrated into synovial fluid effectively achieving peak concentrations within 30 minutes to one hour. Synovial fluid antibiotic concentrations at 2 hours were equal to or higher than simultaneous serum levels. This relationship persisted thereafter. Penetration of antibiotics into infected joints was dependent primarily on serum concentration and was not altered importantly by the presence of acute chronic or previous infection. Antibiotic doses employed were equivalent to clinical usage on a weight basis. Penetration of all antibiotics studied was satisfactory for use against their normally intended pathogens.