Seventy year old medical books even.
The military was using it by the end of the forties.
We were still using it when I was in.
It can have pretty potent side effects and a lot of people got a fever or chills from it.
I took hydroxychloroquine (Plaquenil) for years for my rheumatoid arthritis: one 200 mg tablet twice a day, every day, with food. Never had the slightest uncomfortable side effect.
Don't know what the dosage would be for CV19 though.