As a preliminary study of the microbiological effectiveness of parenterally administered penicillin in suppurative arthritis, the need for adapting quantitative methods of bio-assay to joint fluids became apparent. Recently, Jocson4 has shown in humans that penicillin will cross synovial tissue. The distribution of electrolytes between plasma and joint fluids is in dynamic equilibrium obeying the laws of Donnan's equilibrium. The larger molecules, such as albumin, globulin, and mucin, behave differently.It is the purpose of this paper to report a statistically reproducible quantitative method of measuring penicillin in the knee joint fluid of normal rabbits. The relationship of joint fluid concentration to circulating blood serum levels has been studied.
The potassium salt of crystalline penicillin G (benzylpenicillin) with a molecular weight of 372.48 and a theoretical potency of 1,595 units per milligram was chosen because of its widespread clinical usage. Penicillin concentrations were determined by an adaptation