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.