Cycloguanil pamoate, known as CI-501 (Camolar), given as a single intramuscular injection at a dose of 5 mg (base) per kg body weight, was used to determine if the drug acted as a causal prophylactic against a Southern Rhodesian strain of falciparum malaria. A total of 21 prisoner volunteers participated in the study.
Nine volunteers were medicated at intervals ranging from one day before to nine days after exposure to falciparum malaria by the bites of heavily infected Anopheles freeborni mosquitoes. Seven volunteers were used as subinoculees to prove whether or not four of the study cases had subpatent infections. Five volunteers served as controls.
None of the volunteers medicated through the 5th day after exposure developed malaria. The volunteer medicated on the 7th post-exposure day developed a subpatent infection as determined by subinoculation. The man who received his medication on the 9th post-exposure day developed a patent infection; he exhibited a modified clinical attack with low parasitemia.
These results indicate that CI-501 acts as a true causal prophylactic against this strain of falciparum malaria despite the fact that the erythrocytic stages are partially resistant to it.