International collaborative study to establish the 3rd International Standard for Streptokinase

An international collaborative study was organized to calibrate a replacement for the current (2nd) International Standard (IS) for Streptokinase, stocks of which are almost exhausted. Two candidate preparations were assayed against the 2nd IS in a study involving 16 laboratories in 12 countries: preparation 88/824 (coded B), and preparation 00/464 (C and D, coded duplicates). Laboratories could use two methods provided, either a fibrin clot lysis assay or a solution chromogenic method, or an in-house method. Laboratories were encouraged to perform more than one method if possible. With the exception of one laboratory which gave outlying results for preparation 00/464, there was good agreement within and between laboratories and no significant differences between potencies using the different methods employed. This study demonstrates that a solution chromogenic assay is an acceptable format for potency determination of the streptokinase preparations in this study and fibrin is not necessary. It has now been agreed that a solution chromogenic plasminogen activation assay replace the current euglobulin reference method for streptokinase activity determination in the European Pharmacopoeia. Study participants, SSC of the International Society on Thrombosis and Haemostasis and the Expert Committee on Biological Standardization (ECBS) at the World Health Organization approved preparation 00/464 (C,D in the study) as the 3rd IS for Streptokinase with a potency of 1030 IU per ampoule.