FIFTH INTERNATIONAL STANDARD FOR GAS-GANGRENE ANTITOXIN (PERFRINGENS) (CLOSTRIDIUM WELCHII TYPE A ANTITOXIN).

The Fifth International Standard Gas-Gangrene Antitoxin (Perfringens) (Clostridium welchii Type A Antitoxin) was prepared from serum from immunized horses. It was freeze-dried in ampoules each containing 1 ml.Seven laboratories collaborated in assaying its potency in terms of the Fourth International Standard by the intravenous inoculation of mice. The geometric mean value, taking the results of all the laboratories, was 270 International Units per ampoule and the maximum variation between laboratories was 15%.In vitro (lecithinase) tests were also done by three laboratories, giving an average of 261 International Units per ampoule.The dry weight contents of ampoules, determined in three laboratories, varied by less than 3%, with an average of 90.35 mg per ampoule.The standard was stable for 120 hours at 56 degrees C.Each ampoule of the Fifth International Standard for Gas-Gangrene Antitoxin (Perfringens) contains 270 International Units, and one International Unit is contained in 0.3346 mg of the International Standard.