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September 01, 2021

A pill to treat COVID-19? Pfizer takes next step in study of Tamiflu-like drug

If effective, the medication would be given to people shortly after they develop symptoms

Illness COVID-19
Pfizer Antiviral Pill COVID-19 CHARLES GUERIN/ABACA/SIPA USA

Antiviral drugs to treat COVID-19 in pill form are a priority among researchers who hope to offer an accessible medication to people who become infected and show symptoms. Pfizer is entering the next stage of clinical trials on an antiviral drug it hopes can be safely used by a broad population.

Pharmaceutical giant Pfizer is set to expand clinical trials for an oral, antiviral medication that could be taken at home to reduce the severity of COVID-19 symptoms. The drug is viewed as a potentially vital step forward in the treatment of people who have coronavirus infections.

The search for COVID-19 treatments and medications has been multifaceted throughout the pandemic, with many more failures than successes for people who become severely ill.

Alongside its vaccine program, Pfizer has been working on an antiviral pill known as a protease inhibitor. This class of drugs has been effectively used to treat HIV and hepatitis C, preventing viruses from replicating by binding to enzymes that prevent the further production of viral particles in the body.

The company announced Wednesday that it has initiated a later-stage clinical trial for its new antiviral medication and will enroll 1,140 participants to further examine the effectiveness of the drug against COVID-19.

The way the new drug is administered can be compared to the way Tamiflu is taken by people who become symptomatic with the flu. Tamiflu is recommended within 48 hours of the onset of flu symptoms to reduce their severity over the course of the illness, which may be shortened by a few days with the aid of the medication.

Pfizer believes that if its drug proves successful in ongoing trials, it could be used by hundreds of millions of patients in the years ahead as an affordable treatment for COVID-19.

"If successful, [the drug] has the potential to address a significant unmet medical need, providing patients with a novel oral therapy that could be prescribed at the first sign of infection, without requiring hospitalization," Pfizer said in its announcement.

Pfizer's Phase 2/3 trial comes after an early-stage study in March exceeded expectations. The drug was found to reduce viral replication in people with COVID-19 by more than fivefold. Preclinical testing also showed the drug could be effective against all currently known variants of COVID-19.

Pfizer chief scientific officer Mikael Dolsten said the drug appears to have a good safety profile and has not generated any problems in doses up to 500 milligrams twice per day over a 10-day period.

Pfizer CEO Albert Bourla tweeted that the promising drug represents another arm in the fight against COVID-19.

The drug potentially could be helpful for a broad population of patients who have symptomatic cases of COVID-19 but are not hospitalized or at risk of a severe infection. Pfizer is separately conducting a clinical trial on the effectiveness of the drug in people who are at risk of severe illness.

For the next phase of the clinical trial, Pfizer will be testing the antiviral drug in non-hospitalized, symptomatic adults who have a confirmed COVID-19 diagnosis and are not at increased risk of progressing to severe illness. Participants in the randomized, double-blind trial will receive the drug or placebo orally every 12 hours for five days.

The company also plans to test the drug over 10-day periods and among people who have had close contact with a person with COVID-19.

The U.S. government's Antiviral Program for Pandemics has invested more than $3 billion into research and clinical trials for antiviral pills to treat COVID-19. Drugmakers Merck and Roche also have been working on potential antiviral medications to treat and reduce COVID-19 symptoms.

Vaccines have been the primary defense against COVID-19, aiming to immunize people against the coronavirus and prevent them from becoming infected or having a symptomatic illness. Earlier this month, Pfizer's COVID-19 vaccine, branded as Comirnaty, became the first coronavirus shot to be approved by the U.S. Food and Drug Administration

But for people who have COVID-19, proven treatment methods have remained fairly limited.

Among hospitalized patients and others with more serious illnesses, the most common, FDA-sanctioned treatments are remdesivir, an IV-administered antiviral medication, and Regeneron's monoclonal antibody cocktail, a combination of lab-made proteins that mimic the immune system's ability to fight off harmful pathogens such as viruses.

In Regeneron's treatment, the drugs casirivimab and imdevimab are used to target the spike protein of the coronavirus, blocking its attachment and entry into human cells. Monoclonal antibody treatment, administered via infusion or injection, is expensive and has a relatively narrow scope of patients under its emergency use authorization.

An antiviral pill for people with less severe COVID-19 infections could have broad implications for the treatment of a much bigger population. It also may become a desperately needed safety net for people who are unable to be vaccinated.

"If you can get a vaccine, that's great but not all people can be vaccinated," Dr. Michael Teng, a virologist at the University of South Florida, told CBS affiliate 10 Tampa Bay. "There are some people, cancer patients, people undergoing treatment or people genetically that have lower immune response and they can't be vaccinated so it's important to provide later protection for them."

Teng explained that antiviral medications typically need to be formulated for particular viral strains to have maximum effectiveness, meaning drugs in this class may end up requiring changes based on new viral variants.

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