This is a meaningless statement.

For starters, to call a compound "reactive" means it's eager to participate in chemical reactions. I'm unable to discern what you were trying to say, but I'm betting it isn't that.

To continue, yes, at the limit, a sufficient dose of anything will kill you. The difference between the therapeutic dose and the lethal dose is referred to as the therapeutic index: wide is good, narrow is dangerous.

(hydroxy)chloroquine has a fairly narrow therapeutic index at the doses being tested for acute COVID-19 intervention. That's not a property you want in a medicine. It would have to be that much more effective to make up for the risk it poses to the patient.

Most everything has an LD50 value but that often doesn't make any practical difference.

You can construct scenarios where LD50 of water is relevant, say, but it isn't easy to see them in practice I imagine.