Use in ProphylaxisThe use of Diphtheria Antitoxin is not recommended for prophylaxis as its protective effect is of short duration (1 to 2 weeks only) and furthermore, it may cause sensitization to horse sera. Instead, the contacts of Diphtheria patients should receive a dose (0.5 ml) of diphtheria vaccine (Diphtheria vaccine, Adsorbed PTAP) or adsorbed diphtheria- tetanus vaccine (D-T Vaccine, which protects against both diphtheria and tetanus.) and followed after 1 to 2 months with a second dose. Prophylaxis with diphtheria vaccine is gives protection for many years and is practically free from reaction..Use in TreatmentA dose of 10000 IU to 30000 IU of diphtheria antitoxin may be injected intramuscularly in mild to severe cases of diphtheria and upto 100000 IU in severe cases after testing serum sensitivity(see below for reactions to horse serum). In addition and may be administered. It is advised that after recovery from diphtheria, patients should be actively immunized for long term protection by the use of two doses at interval of 1 to 2 months with adsorbed diphtheria vaccine or with adsorbed diphtheria-tetanus vaccine.Reactions to Horse serumInjection of diphtheria antitoxin in horse serum sensitive individuals can produce immediate reaction of acute anaphylaxis which could sometimes be fatal unless immediately countered by injecting 1 ml of 1:1000 adrenaline intramuscularly. Every care should be taken to prevent this reaction. Before injection of diphtheria antitoxin, it is necessary to enquire from the patient: (1) whether he/she has had injections of any serum before, (2) whether there is personal or family history of allergy i.e. asthma, eczema or drug allergy. The sensitivity of the patient to the serum is tested by injecting subcutaneously 0.1 ml of diphtheria antitoxin diluted 1:10 and the patient is observed for 30 minutes for local and general reactions. If the test dose shows either local reaction such as wheal and flare or general anaphylactic reaction such as pallor, sweating, nausea, vomiting, urticaria or fall of blood pressure, these should be treated with 1 ml of 1:1000 adrenaline (which should be always be kept handy) before injecting the main dose of diphtheria antitoxin. Half the dose of adrenaline may be repeated 15 minutes later if necessary