Inhibition of human monocyte function by prophylactic doses of chloroquine

The effect of prophylactic doses of chloroquine on the phagocytic function of human monocytes was studied in young healthy male volunteers. They received placebo, 300, or 600 mg of chloroquine base/week for six weeks. In each subject, the phagocytic function was tested before and at the end of the chloroquine intake period. In the 600-mg chloroquine group, it was also tested six weeks after receiving the last dose. Chloroquine at both doses inhibited the phagocytosis of IgG-coated sheep red blood cells and of zymosan particles. The effect was more pronounced with the 600 mg dose of chloroquine. The phagocytic activity returned to normal values six weeks after the end of treatment.