Hydroxychloroquin is a drug which is licenced for malaria prevention as well as for treatment of rheumatoid arthritis and connective tissue disease (i.e. systemic lupus erythematodes).
At the moment (03/29/20) hydroxychloroquin seems to be the most promising treatment out of the ones which have been mentioned/considered. It has been shown to be effective against SARS-CoV-2 in vitro.
A study from China has shown positive effects on clinical outcomes, as well as viral clearance (Gao J et al. Biosci Trends 2020 Feb 19) . A recent study from France has confirmed the efficacy of hydroxychloroquin to reduce viral load of SARS-CoV-2 (Gautret P et al.Int J Antimicrob Agents. 2020 Mar 20)
Hydroxychloroquin should be administered orally at a dose of 400mg once daily. It has a better safety profile than chloroquin. Beware that cases of cardiomyopathy resulting in cardiac failure, in some cases with a fatal outcome, have been reported in patients treated with hydroxychloroquin.