WARNING HEMATOLOGIC REACTIONS QUALAQUIN® use for the treatment or prevention of nocturnal leg cramps may result in serious and life-threatening hematologic reactions, including thrombocytopenia and hemolytic uremic syndrome/thrombotic thrombocytopenic purpura (HUS/TTP). Chronic renal impairment associated with the development of TTP has been reported. The risk associated with QUALAQUIN use in the absence of evidence of its effectiveness in the treatment or prevention of nocturnal leg cramps outweighs any potential benefit [see WARNINGS AND PRECAUTIONS]. QUALAQUIN (quinine sulfate) is a cinchona alkaloid chemically described as cinchonan-9-ol, 6'-methoxy-, (8&apha;, 9R)-, sulfate (2:1) (salt), dihydrate with a molecular formula of (C 20 H 24 N 2 O 2 ) 2 •H 2 SO 4 •2H 2 O and a molecular weight of 782.96. The structural formula of quinine sulfate is: Quinine sulfate occurs as a white, crystalline powder that darkens on exposure to light. It i...