chloroquine is very common in places where there is Malaria, it is not exactly something that can be used without care :
Common side effects include muscle problems, loss of appetite, diarrhea, and skin rash. Serious side effects include problems with vision, muscle damage, seizures, and low blood cell levels.
and it is cheap
The wholesale cost in the developing world is about US$0.04. In the United States, it costs about US$5.30 per dose.
Though nearly a dozen drugs to treat coronavirus are in clinical trials in China, just one—remdesivir, an antiviral that was in trials against Ebola and the coronavirus MERS—is in full-on trials in the US. Nothing has been approved by the Food and Drug Administration. So a promising drug would be great—and even better, chloroquine isn’t new. Its use dates back to World War II, and it’s derived from the bark of the chinchona tree, like quinine, a centuries-old antimalarial. That means the drug is now generic and is relatively cheap. Physicians understand it well, and they’re allowed to prescribe it for anything they want, not just malaria.