Experimental Chemoprophylaxis of Amebiasis

Abstract

Summary Two amebicidal drugs, Milibis (bismuth glycolylarsanilate) and Diodoquin (5,7-diiodo-8-hydroxyquinoline) were administered in less than the recommended curative doses to human volunteers who, during the period of medication, were periodically challenged with 2,000 to 4,000 viable cysts of Entamoeba histolytica derived from a non-symptomatic carrier. Starting one week before the first of three weekly challenges and continuing for one week beyond the last, daily doses of Milibis ranging from 75 to 500 mg. were tested in groups of 8 individuals, with a like number of controls for each series of tests. All controls became infected within two weeks after the first inoculation. The highest dosage gave complete protection, the least failed entirely, and 5 of the 8 test subjects were protected by a dosage of 150 mg. All of the 8 subjects given 250 mg. daily for 28 days remained negative. Additional trials of 250 mg., using a 21-day course with inoculations of 4,000 cysts given at the end of the first and second weeks of medication, resulted in one apparent failure among 14 test subjects. However, when the same dosage (250 mg.) was given to the infected individual and to 8 infected controls, all of the infections were terminated. Similar experiments with Diodoquin resulted in complete protection of 9 individuals on 650 mg., 4 out of 7 on 325 mg., and 1 out of 3 on 210 mg. daily. In all of 8 individuals given Atabrine (quinacrine hydrochloride) in doses of 500 mg. daily for 2 days followed by 100 mg. daily for 21 days, inoculations resulted in infections as readily as in the controls. Chloroquine given in weekly doses of 500 mg., after loading doses of 500 mg. daily for 3 days, likewise had no apparent prophylactic effect on experimental amebiasis. Under usual conditions of exposure, effective prophylaxis of amebiasis probably can be accomplished by daily administration of 250 mg. of Milibis, or 650 mg. of Diodoquin, one-sixth to one-third the recommended curative doses. In the dosage recommended for suppression of malaria, Atabrine and chloroquine apparently have no prophylactic value against amebiasis.