Abstract
Daraprim [2:4-diamino-5-(p-chlorphenyl)-6-ethyl pyrimidine], or pyrimethamine, is used as an antimalarial drug. It has characteristics of the antifolic and antifolinic acid group of substances.1 In a symposium on Daraprim,2 the essential features of the chemistry, pharmacology, and toxicity were reviewed. Injections into dogs caused reactions similar to those produced by Aminopterin (4-aminopteroylglutamic acid), and a reversible "megaloblastic" transformation of the bone marrow was noted, with lowering of the number of red and white blood cells in the peripheral circulation. When the drug was used in therapeutic doses, in the treatment of malaria, no change in the blood cell count was noted.3 This paper discusses the effect of Daraprim in the treatment of patients with polycythemia vera. A dose of 25 mg. was given daily to six patients. Three reactions were noted: an orderly reduction in the number of red blood cells, no marked changes in the

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