[Comparative efficacy of homologous and heterologous biologicals against diphtheria]

Comparative assessment of efficacy of homologous and heterologous diphtheria antitoxins on the example of diphtheria intoxication.

Homologous hyperimmune sera were obtained through immunization of rabbits and guinea-pigs with diphtheria toxoid according to schedule. Immune rabbit sera contained 70 - 100 IU/mL of antitoxin antibodies and guinea-pig sera contained 60 - 80 IU/mL. Equine diphtheria antitoxin was used as a heterologous one. Measurement of antitoxin level using experimental animals is based on quantitative assessment of ability of studied sera to neutralize specific dermonecrotic effect of diphtheria toxin.

Concentration of antitoxin in blood of different groups of guinea-pigs immunized 2 days earlier with either heterologous equine antitoxin or homologous antitoxin was 0.06 - 0.125. IU/mL. Animals from both groups were completely protected after administration of 5.64 LD50 of toxin. Alongside with it, 50 - 75% of animals which received homologous antitoxin were protected from higher doses of toxin, whereas all animals which received heterologous antitoxin died after administration of higher doses. After administration of identical doses of homologous antitoxin to rabbits its maximal concentration was observed on the next day, was stable up to 5 - 7 days after injection, decreased two-fold to 12th day and did not change further to 15 - 16 days after injection with subsequent another two-fold decrease to 30th day (then was stable for another 5 - 10 days).

Administration of homologous antitoxin compared to heterologous analogue allows to prolong time of circulation of specific antitoxic antibodies in 3 - 4 times.