Q&A On Paxlovid, Pfizer’s COVID-19 Oral Antiviral

For much of the COVID-19 pandemic, there were few effective treatments — and no easy-to-take oral pill to treat infection with SARS-CoV-2, the coronavirus that causes COVID-19. 

That changed when the Food and Drug Administration authorized Paxlovid, an antiviral pill made by Pfizer, at the end of 2021.

The drug had posted impressive results in a randomized controlled trial, which found high-risk patients who took the pills within five days of developing symptoms were nearly 90% less likely to develop severe COVID-19 than those who received a placebo. The trial, which did not include any vaccinated participants, was stopped early because the findings were so good. 

But to start, supplies of Paxlovid were highly limited. Months later, the drug is becoming more widely available, but roadblocks remain in getting the treatment to those who are eligible.

In late April, the Biden administration announced a new push to expand access, including more locations where Paxlovid is available and additional Test-to-Treat sites, or places where patients can be tested and receive and fill a prescription in one visit. The government is also conducting a public awareness campaign and communicating to providers that there is now an abundant supply of the drug.

Meanwhile, some patients and physicians have noticed that at least on some occasions, those taking Paxlovid may get better and test negative, but then test positive again and have their symptoms return once they finish the pills — an unexpected twist during a pandemic that keeps dishing out surprises.

Given the renewed attention to the drug and the curious “rebound” phenomenon, we’ll explain what is known about Paxlovid at this time.

What is Paxlovid?

Paxlovid is the brand name of Pfizer’s oral antiviral treatment for COVID-19. It consists of two sets of pills that are taken together. The primary pill is nirmatrelvir, which is a new protease inhibitor that prevents replication of SARS-CoV-2. It’s paired with an existing drug known as ritonavir, which slows breakdown of nirmatrelvir in the liver to boost levels of that drug in the blood.

The standard course of the drug is to take two nirmatrelvir pills with one ritonavir tablet twice a day for five days, for a total of 30 pills.

As an antiviral, Paxlovid should be taken as soon as possible after someone gets sick, and