Regeneron has stopped enrolling seriously ill Covid-19 patients in a clinical trial of the antibody treatment that US President Donald Trump has hailed as a “cure” for the disease.
Shares in Regeneron fell as much as 3 per cent after an independent data monitoring committee warned that the risks might outweigh the benefits for hospitalised patients on high levels of oxygen.
The move comes after Eli Lilly, which is also developing a Covid-19 antibody treatment, stopped its trial in hospitalised patients earlier this week, when it found this group was unlikely to benefit.
Both companies have submitted applications for an emergency use authorisation to the US Food and Drug Administration for treating patients with mild-to-moderate Covid-19 — a category that included Mr Trump, who fell ill earlier this month.
Dan Lucey, an infectious disease specialist at Georgetown University, said the regulator should convene a committee of external advisers before issuing an emergency use authorisation, which has never been granted for a monoclonal antibody.
“The FDA needs to carefully examine the evidence on safety — and whether the treatments actually work — to avoid the appearance of replicating mistakes it made issuing emergency use authorisations for hydroxychloroquine and convalescent plasma” to treat Covid-19, he said.
The Regeneron trial will continue in outpatients and in hospitalised patients on low or no oxygen, suggesting any safety concerns are limited to the sickest participants. But as the drug is given by a drip, it may be harder to distribute to less sick patients who are not in hospital.
Eric Topol, director of the Scripps Research Translational Institute, said it made sense biologically that the treatment worked to attack the virus earlier on, but did not treat the body’s own potentially overactive immune response to the disease.
“There is a tiny window and it’s the earlier the better,” he said, adding any safety problems in more seriously ill patients did not raise concerns about patients with mild-to-moderate Covid-19.
The trial of the Eli Lilly antibody in hospitalised patients was originally paused because of a potential safety concern in early October. But when the company announced on Monday it was abandoning that arm of the trial, it said differences in safety between groups were not significant.
The US government has already signed contracts for supplies of both treatments, which boost the body’s immune system with artificially created antibodies. Regeneron has a $450m deal to manufacture and supply its antibody cocktail, while Eli Lilly announced earlier this week an initial agreement for $375m.
Mr Trump took Regeneron’s treatment when he was suffering from the disease. In a video in early October, he praised the drug, saying it made him feel good immediately and suggested it was about to be approved. Leonard Schleifer, Regeneron’s chief executive, has occasionally played golf with the president.
Antibody treatments could become an important tool for physicians. Despite investment in drug trials, there are still few options for treating Covid-19, and there are concerns about how well Gilead’s remdesivir, the only antiviral that has been approved by the US regulator, works.
Geoffrey Porges, an analyst at SVB Leerink, said he was “very confident” that antibody treatments would receive emergency approval. He said it could still have a market of about 40 to 50 per cent of hospitalised patients.
Regeneron stock fell 2.6 per cent to $541.31 in Friday midday trading in New York, while Eli Lilly was down 1 .6 per cent to $130.44.