Antimalarial properties of floxacrine, a dihydroacridinedione derivative.

Evaluations of the activities of floxacrine [7-chloro-10-hydroxy-3-(4-trifluoromethylphenyl)-3,4-dihydroacridine-1,9(2H, 10H)-dione] in owl monkeys infected with trophozoites of a chloroquine-quinine-resistant strain of Plasmodium falciparum, a strain of this plasmodium resistant to both of these quinolines and pyrimethamine, or a strain of P. vivax resistant only to pyrimethamine showed that: (i) this compound regularly effected temporary clearance of parasitemia at daily doses of 1.25 to 2.5 mg/kg; (ii) doses required for the cure of established infections were larger by factors of 6 to 64 than those that effected parasite clearance; (iii) there was more than a 10-fold difference in doses required for the cure of infections with the different strains; and (iv) resistance to floxacrine developed rapidly. Evaluations of the activities of floxacrine in rhesus monkeys challenged with sporozoites of P. cynomolgi showed that: (i) 0.625-mg/kg doses administered daily throughout the incubation period provided complete protection against infection; (ii) single 40.0-mg/kg doses delivered 2 h before sporozoite challenge were without prophylactic activity; and (iii) daily doses of 40.0 mg/kg, the maximum tolerated level, productive of a hemorrhagic syndrome in some subjects, would not cure established infections. These observations suggest that the potential contribution of floxacrine to malaria therapy would be limited to the prophylactic area and for practical reasons would be restricted there by the requirement for daily dosage.