Alternative approach and evaluation of three potency assay methods for testing adsorbed tetanus toxoid

Thirteen batches of adsorbed Tetanus Toxoid (TT) from different manufacturers were tested for potency by three different methods viz: (i) An Antibody Induction Method (AIM) developed in mice: (ii) WHO lethal challenge in mice; and (iii) Conventional Antibody Induction (I.P). Method in guinea pigs. The potency results obtained in AIM, by serological evaluation of immunized mice were found identical and correlated significantly with those obtained by WHO recommended lethal challenge test in mice. The potency data obtained in the present study was found comparable with other studies. An AIM in mice thus offers an alternative to lethal challenge tests and can replace guinea pig model. Out of 107 serum samples obtained from immunized guinea pigs in the conventional antibody induction method, 90% samples contained more than 4 units of tetanus antitoxin per ml. End point titres of 42 serum samples belonging to 5 batches of TT also showed much higher tetanus antitoxin content when determined by TN test. The potency data obtained thus suggest revision of the minimum requirement in Indian Pharmacopoeia which is too low and which may be increased as indicated by the present study.