Quinine Sulfate is a type of medicine called an antimalarial. Its main use is in treating established malarial infections, though it can also be used for treating leg cramps.
Malaria is a potentially fatal disease caused by various types of single-celled (protozoan) parasites known as Plasmodium. Plasmodium are carried by mosquitoes and injected into the bloodstream during a bite from an infected mosquito. Once in the blood, the parasites travel to the liver, where they multiply. The parasites are then released back into the bloodstream where they invade the red blood cells and multiply again. An actual attack of malaria develops when the red blood cells burst, releasing a mass of parasites into the bloodstream. The attacks do not begin until a sufficient number of blood cells have been infected with parasites.
Quinine works by attacking the parasites once they have entered the red blood cells. It kills the parasites and prevents them from multiplying further. It is not fully understood how it kills the parasites.
Quinine is used to treat falciparum malaria (the most serious kind, caused by a type of malaria parasite called Plasmodium falciparum). It is also used to treat malaria where the type of infecting organism is unknown or caused by mixed types of Plasmodium. It is not suitable for the prevention of malaria.
Quinine is also sometimes used to treat recurrent night-time leg cramps, for instance in people with arthritis, diabetes or varicose veins. It is thought to prevent muscle cramps by reducing the sensitivity of muscle cells to stimuli that cause them to contract, as well as by prolonging the time it takes for the muscle to contract. It can take up to four weeks of taking quinine before an improvement in leg cramps is seen. If it hasn’t helped after four weeks then it should be stopped.