Pfizer Says Its COVID-19 Pill Is Highly Effective

Brenda Goodman, MA

November 05, 2021

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

An experimental antiviral pill appears to work very well at keeping people who are at high risk of severe COVID-19 from being admitted to the hospital and dying, according to the drug's maker, Pfizer.

The drug — called Paxlovid — was 89% effective, compared to a placebo, at preventing hospitalization or death in patients with COVID-19 who were at high risk of severe complications. The company says it plans to ask the FDA to authorize the drug for emergency use.

The medication appears to work so well that Pfizer has stopped enrollment in the trial of the drug, which works by blocking an enzyme called a protease that the new coronavirus needs to make more copies of itself.

Stopping a clinical trial is a rare action that's typically taken when a therapy appears to be very effective or clearly dangerous. In both those cases, it's considered unethical to continue a clinical trial where people are randomly assigned either an active drug or a placebo, when safer or more effective options are available to them.

In this case, the company said in a news release that the move was recommended by an independent panel of advisers who are overseeing the trial, called a data safety monitoring committee, and done in consultation with the FDA.

"Today's news is a real game-changer in the global efforts to halt the devastation of this pandemic," said Albert Bourla, PhD, Pfizer chairman and chief executive officer. "These data suggest that our oral antiviral candidate, if approved or authorized by regulatory authorities, has the potential to save patients' lives, reduce the severity of COVID-19 infections, and eliminate up to nine out of ten hospitalizations."

In a randomized clinical trial that included more than 1,900 patients who tested positive for COVID-19 and were at risk for having severe complications for their infections, those who received Paxlovid within 3 days of the start of their symptoms were 89% less likely to be hospitalized than those who got a placebo pill — three patients out of 389 who got the drug were hospitalized, compared with 27 out of 385 who got the placebo. Among patients who got the drug within 5 days of the start of their symptoms, six out of 607 were hospitalized within 28 days, compared to 41 out of 612 who got the placebo.

There were no deaths over the course of a month in patients who took Paxlovid, but 10 deaths in the group that got the placebo.

The news comes on the heels of an announcement last month by the drug company Merck that its experimental antiviral pill, molnupiravir, reduced the risk of hospitalization or death by 50% in patients with mild to moderate COVID, compared to a placebo.

The U.K. became the first country to authorize the use of molnupiravir, which is brand-named Lagevrio.

Stephen Griffin, PhD, an associate professor of medicine at the University of Leeds, hailed the success of both new antiviral pills.

"They both demonstrate that, with appropriate investment, the development of bespoke direct-acting antiviral drugs targeting SARS-CoV2 was eminently feasible and has ultimately proven far more successful than repurposing other drugs with questionable antiviral effects," said Griffin, who was not involved in the development of either drug.

"The success of these antivirals potentially marks a new era in our ability to prevent the severe consequences of SARS-CoV2 infection, and is also a vital element for the care of clinically vulnerable people who may be unable to either receive or respond to vaccines," he said.


Merck: "Merck and Ridgeback's Investigational Oral Antiviral Molnupiravir Reduced the Risk of Hospitalization or Death by Approximately 50 Percent Compared to Placebo for Patients with Mild or Moderate COVID-19 in Positive Interim Analysis of Phase 3 Study."

Pfizer: "Pfizer's Novel COVID-19 Oral Antiviral Treatment Candidate Reduced Risk of Hospitalization or Death by 89% in Interim Analysis of Phase 2/3 EPIC-HR Study."

Stephen Griffin, PhD, an associate professor of medicine, The University of Leeds, Leeds, UK


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