Calibration of a replacement preparation for the International Standard for Rabies Immunoglobulin.

A proposed replacement preparation for the International Standard for Rabies Immunoglobulin was calibrated by means of two assay methods, a neutralization test in mice (MNT) and a neutralization test in cell culture (RFFIT). The calibration was made as an international collaborative assay comprising nine laboratories in eight countries. The results obtained in this study confirm earlier observations about occasional unexplainable differences between relative potencies obtained by the two methods. They also confirm the apparent reliability of the RFFIT. Based on the results obtained the proposed replacement preparation has been established as the second International Standard for Rabies Immunoglobulin with a defined unitage of 30 International Units of Rabies Antibodies in each ampoule.