The video was released a day after aides scrapped a possible live nationwide address by Mr. Trump to show him firmly in command after he had returned to the White House from Walter Reed National Military Medical Center, where he received treatment for Covid-19.
The president has been desperate to announce some kind of definitive treatment, or a vaccine, ahead of the Nov. 3 election, in which nearly all polls show him trailing Mr. Biden nationally. and in key states.
The Regeneron antibody cocktail is not the only drug that Mr. Trump was prescribed. He has also been taking the antiviral drug remdesivir, as well as the dexamethasone, a steroid that the World Health Organization and National Institutes of Health only recommend for people suffering from severe or critical cases of Covid-19.
Doctors have declined to say what other medications Mr. Trump is taking as he fights off the virus.
It is impossible to know if the treatment has cured the president or even if he has beaten the disease. Most people with Covid-19 eventually recover, and medical experts have also said that Mr. Trump is most likely still battling it. Dexamethasone, which Mr. Trump first received on Saturday, is known to create a sense of well-being and euphoria in many people who take it, as well as bursts of energy.
Outside medical experts have said the next week will be pivotal because many patients who do poorly take a turn for the worse in the second week after symptoms arise.
With the federal assistance, Regeneron has said it can produce up to 300,000 doses of the treatment, which is expected to be provided to Americans free of charge. It is one of several similar antibody therapies — another is being developed by Eli Lilly — that seek to give people powerful antibodies in the hopes of boosting their immune response.
But although both companies have reported promising early results, clinical trials are still underway and have not been completed. Although Mr. Trump credited the Regeneron treatment with having improved his illness, there is no way to know if a drug is safe and if it works without testing it in large groups of people, some who receive the drug, and some who get a placebo.