The second International Standard for Dihydrostreptomycin.

The National Institute for Medical Research, London, was requested by the WHO Expert Committee on Biological Standardization to establish a second International Standard for Dihydrostreptomycin, since stocks of the first International Standard were depleted. A batch of 500 g of dihydrostreptomycin sulfate obtained in 1961 was distributed into ampoules in 200-mg amounts and dried in vacuo; the ampoules were then filled with dried nitrogen and sealed. The proposed replacement material has been assayed biologically in terms of the first International Standard in seven laboratories in six countries by means of both plate-diffusion and turbidimetric assays.Significant heterogeneity of the potencies obtained by the different laboratories was revealed by statistical analysis; this heterogeneity might be caused by slight differences in the content of streptomycin of the two samples. The material has been established as the Second International Standard for Dihydrostreptomycin with a defined potency of 820 IU/mg. The International Unit of Dihydrostreptomycin is defined as the activity of 0.001219 mg of the Second International Standard for Dihydrostreptomycin.