What is quinine, and what is it used for?

Quinine is a naturally occurring compound (alkaloid) derived from the bark of the cinchona tree. Quinine is used to treat malaria, a disease with high fevers, shaking chills, and flu-like illness. Malaria is caused by microscopic unicellular parasites belonging to the Plasmodium species, and malaria caused by Plasmodium falciparum is the type most likely to result in severe infections that can even lead to death, if not promptly treated. Malaria can, however, be prevented by taking precautions against mosquito bites in malaria-endemic regions.

Malaria is transmitted by the bite of infective female Anopheles mosquitos. Malarial parasites grow and multiply in the human liver first and then get into red blood cells and multiply further. The parasites grow inside the red blood cells, eventually rupturing them and releasing daughter parasites that invade other blood cells. The blood stage parasites cause the malarial symptoms in humans, though the mosquito itself suffers no ill consequences from the parasite.

When a female Anopheles mosquito bites an infected human, the blood stage parasites get into the mosquito. Certain forms of the parasites known as gametocytes, occur in male and female forms, which mate in the mosquito’s gut. After 10 to 18 days, the parasites, in the form of sporozoites, migrate to the mosquito’s saliva, and this is the mosquito’s infective stage. The parasite is transmitted when the mosquito bites another human, to continue the cycle.

Quinine interferes with the ability of the parasites to break down the hemoglobin in the red blood cells for the oxygen and carbohydrates they need to grow and multiply. Consequently, the parasite starves and hemoglobin builds up to toxic levels within the parasite, killing it. Quinine also gets inserted into the parasite’s DNA and disrupts DNA transcription and replication. Quinine works only on the blood stage of the P. falciparum parasites.

Quinine has been used for centuries to treat malaria and is useful in treating malarial infections that are resistant to other antimalarial agents such as chloroquine. Quinine is approved by the FDA for the treatment of uncomplicated P. falciparum malaria. Quinine cannot be used for preventing malaria or to treat severe or complicated P. falciparum malaria. Quinine is also used off-label to treat babesiosis, caused by a tick-borne parasite that infects red cells.