What is Regeneron, the FDA-approved drug used to treat Donald Trump?

A Covid-19 antibody therapy used to treat he US president was approved by the US drug regulator

A Covid-19 antibody therapy used to treat President Donald Trump was approved by the US drug regulator on Saturday for people who have not yet been admitted to hospital because of the disease but are at high risk.

The green light for drug manufacturer Regeneron came after Regen-Cov2, a combination of two laboratory-made antibodies, was shown to reduce Covid-19-related hospital admissions or emergency room visits in patients with underlying conditions.

"Authorising these monoclonal antibody therapies may help outpatients avoid hospitalisation and alleviate the burden on our healthcare system," said Stephen Hahn, commissioner of the Food and Drug Administration.

Leonard Schleifer, Regeneron's president and chief executive, said the move was "an important step in the fight against Covid-19, as high-risk patients in the United States will have access to a promising therapy early in the course of their infection".

Regeneron's antibody treatment is the second synthetic antibody treatment to receive emergency use approval from the FDA after a similar therapy developed by Eli Lilly was granted the status on November 9.

What do antibody treatments do? 

The human immune system naturally develops infection-fighting proteins called antibodies – but because not everyone mounts an adequate response, companies such as Regeneron and Lilly manufactured lab-made solutions.

They work by binding to a surface protein of the Sars-Cov-2 virus and stopping it from invading human cells.

The FDA said the data supporting Regeneron's emergency use approval came from a clinical trial involving 799 outpatients with mild to moderate symptoms of Covid-19.

For patients who were at high risk because of a variety of underlying conditions – from obesity to old age to diabetes – hospital admissions and emergency room visits occurred in 3 per cent of patients who received the intravenous treatment.

This compared with 9 per cent in placebo-treated patients.

Patients treated with the drug also had lower levels of virus remaining compared with those on the placebo.

How soon will it be available? 

The company said it expects to have doses for 80,000 patients ready by the end of November and approximately 300,000 patients in total by the end of January 2021.

These will be available to US patients at no out-of-pocket cost under the terms of a US government programme.

But with cases surging across the US and around the world, that means access will not be widespread. The US has eported more than 360,000 new Covid-19 cases in the past two days alone.

The recommended dose is 1,200 milligrams of each of the two antibodies, for a total of 2,400 milligrams, in a single infusion.

Regeneron has received more than $450 million from the US government for its Covid-19 drug development efforts under Operation Warp Speed.

So-called monoclonal antibodies are a relatively new class of drug and are considered highly promising.

Last month, an antibody drug developed by Regeneron against the Ebola virus received full FDA approval, the next step after emergency use approval.

In the case of Covid-19, Regeneron first found two antibodies that were highly effective against the Sars-CoV-2 virus, one from a mouse whose immune system was modified to be human-like, the other from a person.

They then harvested the immune cells that made those antibodies and grew them in a lab, to be able to create a mass treatment.

Covid-19 vaccines, such as those developed by Pfizer and Moderna, work by training the immune system to make its own antibodies so they are prepared when they encounter the virus.