Disc-agar diffusion microbiological assay procedure for determining serum and urine levels of sulfacytine and other sulfonamides.

A reasonably precise, reproducible, and sensitive microbiological procedure for directly assaying sulfacytine and other sulfonamides as antibacterially active drugs has been developed by appropriately modifying the standard disc-agar diffusion technique. Blood and urine levels as low as 3 mug/ml may be determined through the use of a strain of Escherichia coli and a chemically defined agar medium devoid of sulfonamide antagonists. Results indicate that this assay method should be a useful adjunct to the Bratton-Marshall colorimetric procedure, by permitting the direct measurement of antibacterially active drug in clinical specimens.