A fluid separated from the coagulated blood of the horse immunized through the inoculation of diphtheria toxin.

Properties : Antidiphtheric serum occurs as a yellowish or yellowish-brown, transparent or slightly turbid liquid, odorless or having a slight odor due to the presence of an antiseptic used as a preservative. The standard of strength, expressed in units of antitoxin power, must be that approved or established by the United States Public Health Service.

A modification of antidiphtheric serum in concentrated form, known as antidiphtheric globulins, is now being used extensively. This is made by the removal, by precipitation with neutral salts, of most of the constituents of the serum except that fraction of the globulins bearing antitoxic potency.

Action and Uses: Antidiphtheric serum neutralizes the toxin of diphtheria and is employed both as a curative and as a prophylactic agent in that disease.

Dosage: The dose of diphtheria antitoxin is measured by antitoxic units. From 500 to 1,000 units are commonly given as an immunizing or prophylactic dose. For curative treatment from 3,000 to 10,000 units may be given as an initial dose and repeated at intervals of from six to twenty-four hours, if no improvement results. In urgent cases it may be given intravenously.