President Donald Trump speaks in the Oval Office on September 17, 2020.

US President Donald Trump is taking Regeneron's experimental antibody drug after testing positive for the novel coronavirus.

On Friday, the American president said that he and US First Lady Melania Trump tested positive for the virus and began isolating. The White House has said that both are "well at this time," and The New York Times reported that the president has mild, cold-like symptoms.

Trump, 74, is at an increased risk for a more serious case of Covid-19 because of his age, weight, and sex.

In a memo released Friday, White House physician Sean Conley said Trump has received an injection of eight grams of Regeneron's antibody drug. The New York biotech started clinical trials on June 11 for the experimental treatment, called REGN-COV2.

The physician's statement noted Trump "remains fatigued but is in good spirits. Conley also noted the president has also been taking zinc, vitamin D, famotidine, melatonin, and a daily aspirin.

Regeneron's drug is an experimental treatment still in clinical trials. On September 29, the company released a description of early results from the first 275 volunteers in the non-hospitalised patient study.

Chief Scientific Officer George Yancopoulos said the data confirmed the company's belief that the drug is most likely to benefit people who did not mount an immune response before taking the drug. But trials are still ongoing, as the early results are not conclusive proof of efficacy.

What's been working to treat Covid-19

Since the start of the coronavirus pandemic, we've learned a lot about how to treat Covid-19, the disease caused by the novel coronavirus.

The US Food and Drug Administration (FDA) has given emergency use authorisation to two coronavirus treatments: the antiviral remdesivir, and convalescent plasma, or blood infusions from recovered patients.

Others, including the steroid dexamethasone, have shown promise in patients with acute infections.

Treatments created to specifically fight the novel coronavirus have shown some promise in early studies, but none are yet approved by regulators in the US for wide use.

Some treatments haven't proven useful, including hydroxychloroquine

We've also learned more about what's less effective at treating Covid-19.

Throughout March and April, Trump consistently touted the prospects of hydroxychloroquine by name. In a March 21 tweet, Trump claimed that a combination of the drug with an antibiotic called azithromycin has "a real chance to be one of the biggest game changers in the history of medicine."

Hydroxychloroquine was first approved in the 1950s to treat malaria and is now widely prescribed to treat certain inflammatory conditions like lupus. In the early days of the pandemic, research showed it could inhibit the virus from spreading in test tubes, supporting the launch of clinical studies to see if it works in humans.

Early studies from France and China encouraged many doctors, as well as Trump, by appearing to show promising signs that the drug may work. The FDA issued an emergency approval to treat hospitalised patients in late-March. A top-ranking government official later claimed there was political pressure put on the agency to green-light the drug. 

These initial findings were severely flawed by the limitations of the studies. The trials enrolled tiny groups of patients or lacked a control group to compare the results against. Studies that enrolled more people and tested the pills against a placebo group consistently found no benefit for hydroxychloroquine.

These negative trial results, which have been published in top peer-reviewedmedicaljournals, found hydroxychloroquine didn't prevent Covid-19 in people exposed to the virus, nor did it help hospitalised patients recover faster.

For instance, a UK-based study enrolling more than 11,000 patients found in June no beneficial effect in using hydroxychloroquine to treat hospitalised patients. Another study led by University of Minnesota researchers recruited more than 800 volunteers who had recently been exposed to the virus. They randomly took either hydroxychloroquine or a placebo as a preventive treatment, and researchers found no meaningful benefit among those taking the malaria pills.

In June, the FDA revoked the emergency use authorisation for hydroxychloroquine and chloroquine. In its statement explaining the reversal, the FDA noted serious heart-related side effects the treatment can cause. The agency concluded those risks do not outweigh any potential benefits in treating Covid-19.

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