April 8, 2020. I continue my previous discussion. If you are sick enough to see a doctor, you may be prescribed hydroxychloroquine, in a large dose, to treat COVID-19. The point I would like to make, is that HCQ (and chloroquine and quinidine) is synthesized in the lab. The product is made up of four equal amounts of different stereoisomers, only one of which is the correct three dimensional to work at the enzyme or binding site. The other three enantiomers are probably competitive inhibitors of the desired molecule. This makes the synthetic drug much less potent that the pure correct molecule. One effect is that a much higher dose is needed, as in the case of HCQ, hundreds of milligrams.

Quinine, from a natural source, is the pure active drug l-quinine enantiomer. Thus, there is much higher potency, and no competitive inhibition by unwanted stereoisomers. My point of reconsideration in the light of prophylaxis, is that a smaller dose may be beneficial at the time of exposure for prophylaxis, as the initial viral exposure is usually low compared to active viral infection. L-quinine is readily available over the counter, and inexpensive. L-quinine has been used in low dose, safely for over 400 years, for the prevention of malaria. It has proven antiviral properties against several single stranded RNA viruses. One glass of tonic water may be enough prophylaxis required per day, and it may be better than nothing. (Juniper berry flavoring in gin has also been investigated as an antiviral)(Do not take if pregnant, have cardiac dysrhythmias, have QT prolongation, are allergic, etc. Ask your doctor, etc.)