What we know about Paxlovid (PF-07321332; ritonavir): oral antiviral against COVID-19 | New COVID-19 Medicine



Article reviewed by Dr. Jan de Witt

Article last updated on 29/11/2021


Paxlovid is an antiviral administered orally to patients who are ill with COVID-19 or have been exposed to the coronavirus SARS-CoV-2 and are at risk of developing severe illness. The manufacturer, pharmaceutical and biotechnology giant Pfizer, developed it to potentially help patients avoid severe illness which can lead to hospitalization and death. It is meant to be administered at the first sign of infection.

Paxlovid is not yet available, but is under evaluation by regulatory bodies around the world like FDA (in the United States) and EMA (in the European Union). Learn more by jumping to the section "Accessing Paxlovid”.

What is Paxlovid (PF-07321332; ritonavir)?

Paxlovid (PF-07321332; ritonavir) is an orally administered medication designed to stop the coronavirus SARS-CoV-2 from replicating by blocking the activity of a key enzyme that the virus uses to replicate inside cells.

A course of treatment consists of 30 pills administered over five days. The treatment can take place at home, it’s not necessary for a patient to be under supervision in a hospital over the course of the treatment.

How does Paxlovid (PF-07321332; ritonavir) work?

Mechanism of action

Paxlovid consists of two protease inhibitors, PF-07321332 and ritonavir. PF-07321332 is designed to block the coronavirus SARS-CoV-2 from multiplying, while ritonavir slows the breakdown of PF-07321332 in the body in order for it to remain active in the body for a longer time and at higher concentrations to help combat the virus.

Protease inhibitors are commonly used to treat HIV and hepatitis C. The origins of Paxlovid date back to the SARS epidemic in 2003 when PF-07321332 started being investigated as a potential therapy in combination with ritonavir (a booster of other protease inhibitors, commonly used with HIV medications and approved in the US for the purpose in 1996) and since the COVID-19 pandemic, 210 researchers have worked on Paxlovid for SARS-CoV-2.

Clinical trial

The latest clinical trial conducted by Pfizer on Paxlovid included 1219 adults from clinical trial sites across North and South America, Europe, Africa, and Asia. Trial participants were elderly or had an underlying health condition which increased the risk of serious illness and had mild to moderate symptoms of COVID-19. Participants were randomised 1:1, with half being administered a Paxlovid pill and the other half receiving a placebo pill every 12 hours for a total of five days, starting treatment within three days of developing symptoms.

According to Pfizer, it found that, among participants who were administered the drug within three days from the onset of symptoms, the risk of COVID-19 related hospital admission or death was 89% lower in the Paxlovid group than the placebo group. When including participants who started the treatment on the fourth or fifth day, Paxlovid reduced the risk of hospitalization or death by 85%. Overall, 0.8% of those given Paxlovid were hospitalised, compared with 7% of patients who were given a placebo, and 0 deaths occurred among patients who received Paxlovid, while 1.6% of the patients who received placebo died.

Safety concerns

The combination of PF-07321332 and ritonavir might be difficult to tolerate by some people due to ritonavir’s potential to affect how other medications are metabolized by the body. Many medicines should not be administered at the same time as Paxlovid, such as drugs for heart disease, immune conditions or pain relievers as they can cause interactions.

Molnupiravir, another COVID-19 pill, has caused concerns among experts due to a study that suggests that it could cause mutations in human DNA (while it’s designed to only cause mutations in virus RNA). There is no evidence of PF-07321332 causing DNA genetic mutations according to preclinical studies.

What is the approval status of Paxlovid (PF-07321332; ritonavir)?

At the time of writing, 29 November 2021, no national regulatory organism has yet approved Paxlovid.

EMA is currently reviewing the data submitted by Pfizer on Paxlovid’s efficiency, quality and safety in order to support national authorities who may decide to use it for COVID-19 in emergency use settings.

The FDA is also analysing the data that Pfizer submitted for unvaccinated people at high risk to authorize Paxlovid to treat people with COVID-19 who are at high risk of severe disease. The FDA will decide who will be eligible to receive the pill.

Once approved, the US plans to buy 10 million courses of treatment and the UK already ordered 250.000 courses.

On 16 November 2021, Pfizer announced that the company made an agreement with Medicines Patent Pool, a nonprofit backed by the United Nations, to grant them a royalty-free license for Paxlovid that would allow manufacturers to produce and sell the drug inexpensively in 95 developing countries, mostly in Africa and Asia, after the drug is approved in those countries. However, the agreement excludes some of the poorer countries that have suffered high losses due to COVID-19, which includes Brazil, Cuba, Iraq, Libya and Jamaica. They, and countries like China and Russia who were also excluded, will have to buy the drug directly from Pfizer.

Accessing Paxlovid (PF-07321332; ritonavir)

Paxlovid is currently being reviewed by the FDA in the United States and the EMA for the European Union. Even if it takes longer to get approved in your country, once it has approval somewhere in the world, you will be able to access it as there are regulations that allow for medicines to be imported in countries where they are not currently approved.

Patients with life-threatening or debilitating diseases have the right to access, purchase, and import medicines with the help of their treating doctors.

Patients and their doctors can do this on the compassionate use or named patient import regulations basis, a legal exception of the general rule that a medicine can normally only be accessed after market authorisation/approval (whatever wording we use) in the country where the patient lives. This exception allows patients to in a legal, ethical and safe way access and get medicines that are not yet approved in their country.

Read more about the "named patient basis” here (EMA).

Once the drug is approved, we are committed to source it so we can help you access and buy Paxlovid (PF-07321332; ritonavir) no matter where you live.

Upcoming medicines for COVID-19

In November 2021, the EMA recommended authorising Ronapreve (casirivimab/imdevimab) and Regkirona (regdanvimab) for mild to moderate COVID-19 illness.

Other drugs under review by the EMA are:

  • Kineret (anakinra)
  • Lagevrio (molnupiravir)
  • Olumiant (baricitinib)
  • RoActemra (tocilizumab)
  • Xevudy (sotrovimab)
  • Evusheld (tixagevimab / cilgavimab)

Contact Patient Support

If you have any questions or need any help, contact our Patient Support Team. We will get in touch with you within 24 hours from Monday to Friday between 9:00 and 18:00 CET.