A method for the manufacture of a sterile intravenous or intramuscular formulation of artesunic acid and the formulation are the subject of this invention. First the artesunic acid powder is sterilized with ethylene oxide and placed into a sterile container. The contained sterilized powder is then dissolved in sterile sodium phosphate buffered solution to produce an injectable intravenous or intramuscular formulation. The sodium phosphate dissolves and dilutes the artesunic acid powder without caking or frothing resulting in an improved drug product. The invention also relates to the formulation and a method of treating a patient with either uncomplicated or severe and complicated malaria.