Chloroquine is two to three times as toxic in animals as hydroxychloroquine, even though
various single and repeated oral dosage regimens in man have given nearly identical
plasma level curves. Tissue distributions are qualitatively similar for both drugs in albino rats—
namely, bone, fat, and brain< muscle< eye< heart< kidney< liver< lung< spleen< adrenal—
but the absolute distribution values are about 2.5 times higher for chloroquine. The
metabolism of chloroquine and hydroxychloroquine differs only in that the latter drug gives …