The International Standard for sisomicin.

An International Standard for Sisomicin has been established on the basis of a collaborative assay. There were seven participating laboratories in seven countries. The activity of the contents of each ampoule of the International Standard of Sisomicin is defined as 35,200 International Units of Sisomicin.

The International Standard for Amikacin.

An International Standard for Amikacin has been established on the basis of a collaborative assay. Seven laboratories, in seven countries, took part. Each ampoule of the International Standard of Amikacin is defined as containing the activity of 50 600 International Units of Amikacin.

Control of the composition of gentamicin sulphate by proton magnetic resonance spectrometry.

The proportions of the main components present in gentamicin sulphate complex, gentamicins C1, C1a and C2, can be monitored by 1H nuclear magnetic resonance (nmr) spectrometry. The method depends on measurement of the peak heights of signals for N-methyl and C-methyl groups present in all three components and of those present in C1 and C2 only, followed by calculation of peak height ratios to control composition within acceptable limits. The precision and reproducibility of the method have been established through two collaborative studies each involving seven laboratories. In the second study, with an improved procedure, the mean variance between laboratories with 10 samples was 3.4 X 10(-4) for the N-methyl ratio of the peak at delta 2.75 to that at delta 2.95, and 1.25 X 10(-3) for the C-methyl ratio of the peak at delta 1.25 to that at delta 1.35. Within laboratories the mean variance for triplicate determinations was 7.4 X 10(-5) and 8.9 X 10(-5) respectively. The data presented here form the experimental basis for the test controlling the composition of gentamicin sulphate in the British Pharmacopoeia 1973: Addendum 1975, and for the introduction into the British Pharmacopoeia of nmr spectrometry as an analytical technique. The reference standards and all batches of gentamicin sulphate intended for therapeutic use in the United Kingdom examined by this procedure comply with the limits laid down.

The international standard for colistin.

An International Standard for Colistin has been established and the International Unit defined as the activity contained in 0.00004878 mg of this preparation. The unit was defined on the basis of a collaborative assay in which nine laboratories from six different countries participated. The material used to prepare the international standard had been manufactured in Japan; it was shown to have a composition similar to that of material produced in Europe and to be suitable for the assay of colistin from the existing sources of manufacture.

The international reference preparation of colistin methane sulfonate.

The international unit of colistin methane sulfonate has been defined by collaborative assay as the activity contained in 0.00007874 mg of the international reference preparation. The definition was based on results from 7 laboratories in 5 countries which carried out assays against their existing national standards. Because of the complex heterogeneity in composition of this antibiotic the international reference preparation was not designated as an international standard.

The second international reference preparation of lymecycline.

The second International Reference Preparation of Lymecycline was established. Nine laboratories in 8 countries collaborated in assaying its potency in terms of the first International Reference Preparation, of which stocks had become exhausted. The best estimate of potency was taken to be 948 IU/mg, which was the unweighted geometric mean of a total of 124 assays. On this basis, the International Unit of lymecycline was defined as the activity contained in 0.0010548 mg of the second International Reference Preparation.

The second international reference preparation of procaine benzylpenicillin in oil with aluminium monostearate.

The second International Reference Preparation of Procaine Benzylpenicillin in Oil with Aluminium Monostearate was established in replacement of the first international reference preparation. The blood-level duration test (WHO Requirements for Biological Substances, No. 9), used to evaluate batches of manufactured material in relation to this reference preparation, was revised to relate to the new reference preparation. Thus a batch now passes the test if the lower confidence limit of the ratio is greater than 0.45, instead of 0.50-the value that related to the first international reference preparation. This change will ensure that material passing the test in the future will be of the same quality as in the past.

The second international standard for tetracycline.

A second international standard has been established to replace the first International Standard for Tetracycline, stocks of which were depleted. The International Unit of tetracycline is defined as the activity contained in 0.00101833 mg of the second International Standard, corresponding to a potency of 982 IU/mg. These values were assigned on the basis of the results of an international collaborative assay carried out by laboratories in 19 countries. Most of the assays were by diffusion techniques; a few were by turbidimetric methods. Both procedures gave statistically valid assays but there was some heterogeneity of repeated estimations within a laboratory and also some heterogeneity of the mean estimates from each laboratory. The agreed defined potency was the unweighted mean of 281 individual assays; the confidence limits were 978-986 IU/mg.