Thiostrepton Click to View Image C72H85N19O18S5 1664.89[1393-48-2]. »Thiostrepton is an antibacterial substance produced by the growth of strains of Streptomyces azureus(Fam.Streptomycetaceae).It has a potency of not less than 900USP Thiostrepton Units per mg,calculated on the dried basis. Packaging and storage— Preserve in tight containers. Labeling— Label it to indicate that it is for veterinary use only. USP Reference standards á11ñ USP Thiostrepton RS. Identification,Infrared Absorption á197Kñ. Loss on drying á731ñ Dry about 1g of sample in vacuum at 60for 3hours:it loses not more than 5.0%of its weight. Residue on ignition á281ñ: not more than 1.0%. Assay— Proceed as directed under Antibiotics—Microbial Assays á81ñ,preparing the Test Dilutionas follows.Transfer about 60mg of Thiostrepton,accurately weighed,to a beaker.Add about 125mLof dimethyl sulfoxide,and stir with a magnetic stirrer until dissolved (about 5minutes).Transfer this solution to a 200-mLvolumetric flask,washing the beaker and the stirring bar with dimethyl sulfoxide.Add the washings to the volumetric flask,dilute with dimethyl sulfoxide to volume,and mix.Dilute this solution quantitatively with dimethyl sulfoxide to obtain a Test Dilutionhaving a concentration of thiostrepton assumed to be equal to the median dose of the Standard. Auxiliary Information— Staff Liaison:Ian DeVeau,Ph.D.,Senior Scientist Expert Committee:(VET)Veterinary Drugs USP28–NF23Page 1918 Phone Number:1-301-816-8178