This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
Antitoxin serum diminishes all the symptoms of diphtheria, and in particular it greatly lessens the liability to sudden heart failure. If the diphtheria toxin be administered to animals fatty degeneration of the heart is found after death, but if they have also had antitoxin this is absent. Both clinical and experimental evidence show that after antitoxin is given, although the bacilli continue to exist in the throat, the formation of membrane ceases and that which is present rapidly disappears; therefore laryngeal diphtheria rarely follows faucial if antitoxin is used early, the patient becomes less anaemic, his pulse improves, and his temperature may fall a little, although this is less influenced by antitoxin than are the other symptoms of diphtheria. The maximum effect of the antitoxin is not seen until twenty-four hours after injection. All reliable collections of cases show that the mortality, especially in children, is much less when the antitoxin is used. It should be given at the earliest possible moment, even if it is only likely that the patient is suffering from diphtheria, for the number of fatal cases is less when antitoxin is used early in the illness. The benefit is more marked in laryngeal than in other varieties of diphtheria, the mortality of tracheotomy cases falling by one half. The frequency of the occurrence of paralysis is not diminished, but the percentage of recoveries in cases with paralysis is slightly increased.
Symptoms of poisoning are sometimes seen after this antitoxin has been given, but they are unimportant. They are not due to the antitoxin in, but to some other constituent of the serum, for they may follow when the simple serum of animals is injected into the human subject. The most common is a rash, met with in about 35 per cent. of the patients injected; it may appear as late as the end of the third week after injection, but it is usually seen at the end of the first week. In a few cases a second rash is observed after the first has faded. Usually it is a mere erythema, but it may be papular or uticarial. Commonly it disappears in three days. Pains in the joints and slight swelling of them are occasionally present and finally somewhat rarely there has been observed an irregular temperature range and consecutively emaciation and death; evidently pointing toward an acquired septicaemia. Further in a few cases an early fatal result has been reported. Browne and Benda both have shown that in a fatal issue, nephritis, in the majority of cases, is the cause of death, and clinically haemorrhagic nephritis is by no means rare. Inasmuch as this remedy militates solely against the infection of the Klebs-Loeffler bacillus and clinically most cases of diphtheria are cases of mixed infection, the usual local antiseptic and general supporting measures must not be omitted. The danger of antitoxin lies in the horse-serum, for, many years before antitoxin was made, the results of injection of an alien serum had been pointed out. Concentrated serums then should be preferred in that they give the largest amount of antitoxin with the smallest amount of serum.
So far as prophylaxis is concerned, the question is still sub judice, many failures are reported, and indeed instances of reinfection have occurred even after suitable doses of antitoxin have been used during a previous attack.