Tetanus antitoxin is prepared by hyperimmunising horses with tetanus toxin. Blood plasma obtained from the hyperimmunised horses which is rich in antibodies to tetanus toxin, is enzyme refined purified and concentrated. The antitoxin has the specific power of neutralising the toxin secreted by Clostridium tetani, the causative organism of tetanus.

A dose of 1500 international units of tetanus antitoxin should be injected subcutaneously or intramuscularly, after testing for serum sensitivity (see below for reactions to horse serum). It should be injected as soon as possible after tetanus prone injury, such as wounds contaminated with soil, dirt etc. Adequate surgical treatment of wounds with the use of suitable antibiotics should be carried out in addition to the prophylactic injection of antitoxin, if the patient is sensitive to serum or has been actively immunised previously with tetanus vaccine (adsorbed) the patient should receive the dose of tetanus vaccine(adsorbed) only and not tetanus antitoxin. The use of antitoxin gives protection for 1 to 3 weeks only. While tetanus vaccine gives long time immunity and is cheaper and practically free from reactions. It is also adviced that simultanously with the administration of the prophylactic dose of tetanus antitoxin active immunization should be started. This is done by injecting at the same time in another arm, 0.5ml of adsorbed tetanus vaccine (Tet./Vac./P.T.A.P.) since adsorbed tetanus vaccine is able to actively immunize against tetanus even in the presence of tetanus antitoxin (B.J.Vakil et al Ind. J.Med. Research, 1968 Vol.56 pp 1188-1201). A second dose of 0.5ml adsorbed tetanus vaccine only is to be injected between 1 to 2 months after the first dose of vaccine and a third dose 6 to 12 months after the second dose to produce adequate long term protection.