Studies of the inhibition by various metabolites of the antitoxoplasmic action of pyrimethamine and sulfadiazine in acute mouse toxoplasmosis, alone and in combination, resulted in the following findings:
1.p-Aminobenzoic acid completely antagonized the effect of sulfadiazine and partially antagonized the effect of pyrimethamine. It also partially inhibited the effect of the drugs in combination.
2.Folic acid incompletely antagonized the effect of sulfadiazine, but did not antagonize the effect of pyrimethamine. It also had no effect upon the drugs when given in combination.
3.Folinic acid did not materially antagonize the action of the combination of pyrimethamine and sulfadiazine or of the drugs individually.
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