The penetration of trimethoprim and sulphamethoxazole into synovial fluid

A group of six patients with non-infected synovial effusions requiring diagnostic or therapeutic aspiration, were given a short oral course of 'Septrin' (two tablets bd for two doses, each tablet containing 80 mg of trimethoprim plus 400 mg of sulphamethoxazole). Serum and synovial fluid (SF) were sampled frequently following antibiotic administration. It was found that concentrations of trimethoprim in SF approached serum levels after a short lag time (about 3 h) and thereafter approximated to the serum levels, whereas sulphamethoxazole did not as readily penetrate into SF. With the regimens used MIC levels for trimethoprim were achieved in SF, which suggests that this drug could be usefully prescribed in normal doses for the treatment of septic arthritis due to bacterial infection.