After co-developing one of the world’s most widely used COVID-19 vaccines, Pfizer announced positive trial results on Friday for its investigational antiviral pill, revealing that the pill could cut the risk of hospitalization and death by 89 percent. The drug, called Paxlovid (a combination of PF-07321332 and ritonavir), is among the first orally administered antivirals against SARS-CoV-2, as other authorized or approved antivirals, such as remdesivir, are administered through intravenous (IV) injection.
The news from Pfizer comes on the heels of Merck winning authorization for its COVID-19 oral antiviral molnupiravir in the UK to make it the world’s first authorized oral pill to treat the infection. Merck developed the antiviral in collaboration with Ridgeback Biotherapetics and Sharpe and Dohme (MSD). It was shown to reduce the risk of COVID-19-related hospitalizations and deaths by 50 percent.
Pfizer’s results come from an interim analysis of the Phase II/III EPIC-HR (Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients) randomized, double-blind study of non-hospitalized adult patients with COVID-19 at risk of developing severe disease.
In a statement, Pfizer said it will discontinue further enrolment in the study “due to the overwhelming efficacy demonstrated in these results” at the recommendation of an independent data monitoring committee and after consultation with the US Food and Drug Administration (FDA). The interim analysis was based on data from about 1,200 participants; Pfizer had initially planned to enrol 3,000 individuals in its study. The company also revealed that it plans to submit the data to the FDA as part of its ongoing rolling submission for emergency use authorization (EUA).
The Paxlovid treatment consists of two pills of the protease inhibitor Paxlovid and one of the antiviral ritonavir; the latter prolongs the action of Paxlovid at high concentrations. Ritonavir blocks viral replication and is used for treating and managing HIV.
The treatment pack is given twice a day for five days and within five days of symptoms onset.
The interim analysis of the EPIC-HR trial demonstrated an 89 percent reduced risk of hospitalization or death from COVID-19 compared with placebo among a total of 1,219 trial participants enrolled by the end of September 2021. Less than one percent (0.8 percent) of patients who received Paxlovid within three days of symptoms onset had to be hospitalized compared with seven percent in the placebo group.
There were no deaths in the Paxlovid group while seven deaths occurred among those that were hospitalized and received placebo. The results were similar for the administration of the drug combo within five days of symptoms appearing (one percent versus 6.8 percent hospitalizations in the antiviral treatment versus placebo arms, respectively).
Most side effects were mild and comparable to those after receiving placebo.
The EPIC-HR study began enrolling participants in July 2021.
“Today’s news is a real game-changer in the global efforts to halt the devastation of this pandemic. 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,” said Albert Bourla, Chairman and chief executive officer of Pfizer said in the company statement released on Friday.
“Given the continued global impact of COVID-19, we have remained laser-focused on the science and fulfilling our responsibility to help healthcare systems and institutions around the world while ensuring equitable and broad access to people everywhere.”
Pfizer is planning to complete two other studies of the drug by the end of the year. It remains unknown how much it would cost if authorized for use.
While Merck and Ridgeback may be off to the races with molnupiravir, as the companies say they are on track to producing 10 million courses of the treatment by the end of the year, it’s not known what Pfizer’s production plans are for Paxovid pending authorization.