Fowler's solution is a solution containing 1% potassium arsenite (KAsO2), and once prescribed as a remedy or a tonic. Thomas Fowler of Stafford, England, proposed the solution in 1786 as a substitute for a patent medicine, "tasteless ague drop". From 1845, Fowler's solution was a leukemia treatment.
At 1905, inorganic arsenicals, like Fowler's solution, saw diminished use as attention turned to organic arsenicals, starting with Atoxyl. Still, into the late 1950s, Fowler's solution—also termed liquor potassii arenitis, Kali arsenicosum, or Kali arseniatum—was prescribed in the United States for a wide range of diseases, including malaria, chorea, and syphilis.
As arsenical compounds are notably toxic and carcinogenic—with side effects such as cirrhosis of the liver, idiopathic portal hypertension, urinary bladder cancer, and skin cancers—Fowler's solution fell from use. (In 2001, however, the U.S. Food and Drug Administration (FDA) approved a drug of arsenic trioxide to treat acute promyelocytic leukaemia, and interest in arsenic has returned.)