A Method for Determination of Streptomycin in Body Fluids

The introduction of streptomycin as a chemotherapeutic agent for the treatment of bacterial infections1-4 has emphasized the need for a quantitative method for the determination of the drug in body fluids. In a recent communication, Foster and Woodruff described a method for the determination of streptothricin in aqueous solution. 5 Attempts to apply this procedure directly to the quantitative determination of streptomycin in blood, urine and body tissues were not satisfactory for, among other things, it was found that the blood of certain animal species, as well as man, contains a substance which produced a marked inhibitory effect upon the test organism (Bacillus subtilis). Frequently this substance was present in amounts sufficient to produce a zone of inhibition larger than that obtained with low concentrations of streptomycin. Furthermore, the method of Foster and Woodruff, when applied to the assay of streptomycin, was not sufficiently sensitive to measure accurately concentrations of the drug in serum below 20 units per cc. The foregoing difficulties were largely eliminated by the use of a streptomycin sensitive organism (Staphylococcus aureus SM) which was not inhibited by normal blood, by increasing the pH of the medium and by decreasing the salt concentration. These two latter factors were shown by Foster and Woodruff to influence the activity of streptothricin and later 6 were shown to enhance the activity of streptomycin in culture fluids, etc., when Bacillus subtilis was employed as the test organism. The assay described in this communication is suitable for the determination of streptomycin in blood, urine and tissue fluids of mice, rats, rabbits, dogs, monkeys and man. Materials. A strain of Staphylococcus aureus SM is used as the test organism. The culture is maintained in a uniform condition by daily transfer in F.D.A. nutrient broth at 37°C.