An article I read somewhere was suggesting that doctors should have tried using traditional antibiotics to treat patients instead of intubating them. This of course is strictly anecdotal.
Using traditional antibiotics against a virus is not particularly likely to help. Traditional antivirals are in a number of studies currently.
By my non-expert estimate, remdesivir seems to be the most likely candidate. It's not approved for use in the US yet, but is well on the path: https://www.drugs.com/history/remdesivir.html
That's odd since coronavirus is a virus, not a bacteria, so I wouldn't expect antibiotics to be relevant except insofar as they would suppress opportunistic infections.
By my non-expert estimate, remdesivir seems to be the most likely candidate. It's not approved for use in the US yet, but is well on the path: https://www.drugs.com/history/remdesivir.html