It has recently been proposed that an old, already approved drug typically used for malaria, could be used to treat COVID-19. It has even been suggested for use by governments around the world.
I looked into the research on it and it doesn’t look promising. First, there are no tests in patients. All of the work is on cells growing in test tubes in the lab. The work is shown here in this chart. In the laboratory, high concentrations can stop the virus getting into cells by >80%, which is not bad. Unfortunately, when you compare the blood level achieved in humans when the drug is given orally to the level used in the test tube experiments, the scientists used 100-times as much drug as you can get in your body. It probably doesn’t so much are the very low doses in the body.
This is the nature of research and every bit of new data, if not directly, clinically useful, moves us forward.