A close look at why this old malaria drug could be promising for Covid-19
As COVID-19 ravages the world, scientists are desperately trying to develop a medication to stop the virus (severe acute respiratory syndrome coronavirus 2, or SARS-CoV-2). Dozens of drugs and vaccine candidates are in various stages of development and testing. Among these is chloroquine, a seemingly strange choice as it has been widely used to treat malaria since the 1940s.
Not only is chloroquine effective in treating malaria, it is inexpensive to make and remarkably well-tolerated by most patients (though it poses the same dangers all medications do if taken without the oversight of a doctor). It was such a good drug in the battle against malaria that it was overused, facilitating the emergence of malaria parasites that are resistant to it.
Malaria is caused by a single-celled parasite called Plasmodium. After a mosquito harboring the parasites bites a victim, the parasites make their way to the liver and eventually the red blood cells. Inside red blood cells, the parasites use the hemoglobin as a food source, which is digested in the parasite’s acidic food vacuole. The eventual destruction of red blood cells leads to life-threatening anemia. Consequently, malaria claims the lives of over 400,000 people per year, mostly children under the age of five in sub-Saharan Africa.
How chloroquine kills Plasmodium parasites has long been the subject of research. The drug is capable of binding to heme, which is a toxic byproduct of hemoglobin digestion. The parasite avoids the toxic effects of heme by stacking the molecules into an inert crystal called hemozoin. But when chloroquine binds to heme, hemozoin cannot be made, forcing the parasite to die in its own waste. Further supporting this idea is the fact that chloroquine concentrates in acidic cellular compartments, such as the parasite’s food vacuole.