The discovery of pamaquine, developed by replacing one of the methyl groups of methylene blue by a dialkylaminoalkyl chain, was a landmark in the design of drugs for malaria. It is closely related to primaquine. The administration of pamaquine during the incubation period delayed but did not prevent primary attacks of a New Guinea strain of Plasmodium vivax malaria. Hemolytic anemia after administration of the antimalarial drug pamaquine was reported in patients with Glucose-6-phosphate dehydrogenase (G6PD) deficiency. Pamaquine itself could not be used clinically due to high toxicity.