I mean specifically with regards to treating covid-19, not for other purposes. Sorry if that wasn’t clear. I didn’t say there’s a study that says hydroxychloroquine combined with arithromycin is an ineffective combination, but that unless there’s a scientific reason to assume something will increase the effectiveness of such a possibly lethal drug without exacerbating its negative side effects then there is no reason to start with the assumption that it is safe.

Keep in mind that the lack of rigor in the current pre-peer review literature coming out means that you have to take everything into account and with a grain of salt. For example, a drug showing effectiveness might have been with a mild case that started with a low viral load and wouldn’t have progressed any way (this is just an example, I’m not saying that is the case). Since the therapeutic index is so low, you can’t just dial up the dosage to treat severe cases that actually require pharmaceutical intervention, because it’s a non-starter.

Can you cite it not working for covid-19 in vivo? From what I've found there are early stage trials showing success, plus a few larger anecdotal populations showing bigger success, but nothing that scientifically definitively concludes either way.

Yes, there simply hasn’t been enough time for proper studies to have been made one way or the other [0]. The only “study” showing in vivo efficacy is pretty much a bunch of bunk and has huge issues. It did not report on actual treatment outcomes but only on nasal swab results without a control arm, never mind that covid-19 has been demonstrated to move from upper respiratory down into the lungs in most cases that progress to pneumonia or respiratory distress anyway (so a nasal swab says nothing and can come back negative while the patient is dying of respiratory failure).

[0]: https://www.cebm.net/covid-19/chloroquine-and-hydroxychloroq...

That means your claim that it “only works in vitro” is false, though. The right claim would be “we don’t know yet”.

Also you do a lot of work to make it sound like a foregone conclusion it doesn’t work (appeals to authority in “anyone paying attention”).

The problem is there is now a lot of anecdotal evidence of it working from good sources (teams of doctors on frontlines from around the world). So really you can’t appeal to anyone paying attention.

Yes, so far as we know.