Quinine sulfate is a salt form of quinine, an alkaloid that is derived from the bark of the cinchona tree. It has the chemical formula C20H24N2O2.H2SO4 and is a bitter tasting, white crystalline powder.Quinine sulfate is commonly used as a medication to treat and prevent malaria, a parasitic disease that is transmitted by mosquitos in tropical and subtropical regions. It works by interfering with the growth and reproduction of the malaria parasite in the body. Quinine sulfate is also used as a treatment for nocturnal leg cramps, a condition characterized by painful spasms in the legs during sleep. It is thought to work by decreasing the excitability of the muscle cells, thus reducing the frequency and severity of cramps.