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.

Dihydrostreptomycin Sulfate↗

PubMed1966

The international standard for novobiocin.

The National Institute for Medical Research, London, was requested by the WHO Expert Committee on Biological Standardization to arrange a collaborative assay of the International Reference Preparation of Novobiocin in order to define the International Unit of Novobiocin. The collaborative assay showed that the International Reference Preparation was not suitable for use as an international standard, and a second preparation of 400 g of novobiocin acid was obtained in 1962. This second preparation was distributed into ampoules in 100-mg amounts and dried in vacuum. The ampoules were then filled with dry nitrogen and sealed. This material-the proposed international standard for novobiocin-has been assayed biologically in eight laboratories in six countries by means of plate diffusion assays; it has been assayed against the working standard preparation of the US Food and Drug Administration.The variation in the potencies obtained for the second proposed international standard for novobiocin were small and not significant. The material has been established as the International Standard for Novobiocin with a defined potency of 970 International Units per mg, and the International Unit has been defined as the activity contained in 0.001031 mg of the International Standard.

Bacteria↗

PubMed1965

The international standard for oleandomycin.

At the request of the WHO Expert Committee on Biological Standardization a batch of oleandomycin was submitted to an international collaborative study in six laboratories situated in four countries. In this study the material was assayed by plate diffusion methods, which varied in details of technique and design, against the US Food and Drug Administration's reference preparation for oleandomycin. On the basis of the results obtained the material has been established as the International Standard for Oleandomycin and the International Unit of Oleandomycin is defined as the activity in 0.001176 mg of the International Standard. The US Food and Drug Administration's standard and the International Standard are each part of the same parent batch of oleandomycin and the validity of such an assay has been compared with the more usual assay situation when there is some degree of difference between the preparations under comparison.

Biological Assay↗

PubMedDate not supplied

Attenuation of Eimeria necatrix and E. tenella of U.S. origin by serial embryo passage.

Two lines of Eimeria tenella (PS and FS65) and one line of E. necatrix (FS144) of U.S. origin were passaged in chicken embryos. The embryo-passaged line of E. tenella PS was significantly less pathogenic than the parent line when tested in chickens after 33 embryo passages. After 29 embryo passages, E. tenella FS65 was just as pathogenic to chickens as the parent line. A comparison of the immunogenicity of the embryo-adapted lines and the parent lines in chickens showed that embryo-passaged E. tenella PS and E. tenella FS65 were as immunogenic as parent lines. The embryo-passaged line of E. necatrix FS144 was significantly less pathogenic when tested in chickens after 30 embryo passages. Although there was also some loss of immunogenicity in the embryo-passaged line of E. necatrix, immunity to this parasite could be achieved by increasing the dose of oocysts.

Animals↗