Dr. Kalil is haunted by memories of the Ebola outbreak that ravaged Africa from 2014 to 2016. Then, too, doctors said they could not wait for scientific evidence, and untested drugs were given to suffering Ebola patients by optimistic physicians with noble intentions. In the long run, none of the drugs was ever approved in the United States for treatment of the disease.

Today, hope centers on chloroquine and hydroxychloroquine. These drugs have been tested in the laboratory against many viruses: SARS and MERS — both coronaviruses — as well as H.I.V., dengue, Ebola, chikungunya and influenza. But even when they seemed to work, what succeeded in the test tube did not succeed in real life, Dr. Kalil said.

In fact, the anti-malarial drugs have never been found to work against any viral disease, including Ebola. (Malaria is caused by a parasite, not a virus.) And the drugs have side effects, including damage to the liver and bone marrow, as well as heart rhythm disturbances that could be fatal in older people and young people with serious medical problems.

Even worse, Dr. Kalil said, is the promotion of the antibiotic azithromycin in combination with the anti-malarial drugs to treat Covid-19 patients. Azithromycin also may cause serious heart rhythm problems, and the combination of drugs, Dr. Kalil said, has never been tested for safety in humans.

That is not to say the drugs won’t help patients with the coronavirus, only that whether this is so is unknown.