Paxlovid (“Paxlovid”) is an antiviral drug for treatment of patients with a risk of COVID-19 progression to severe stage,  is developed by the American pharmaceutical company Pfizer.

This is a medicine that consists of two separate pills – nirmatrelvir and ritonavir. The first blocks one of the key SARS-COV-2 proteins work, which is necessary for the virus to create new copies. Ritonavir prevents the breakdown of nirmatrelvir before it has completed its work.

In clinical trials published by Pfizer at the end of 2021, Paxlovid prevented high-risk people from being hospitalized or dying from COVID-19 by almost 90%. Current clinical trials indicate that Paxlovid is approximately 70% effective in people at standard risk for severe COVID-19.

All participants in clinical studies began treatment with Paxlovid within the first five days after symptoms onset. With a later start of therapy, the effectiveness of the drug decreases.

After the first symptoms of COVID-19 appear, the patient should take Paxlovid orally twice a day for five days. One dose of the drug includes three pills – two with nirmatrelvir and one with ritonavir.

Paxlovid’s reception has a number of side effects that must be considered before prescribing. It can also affect on other medications work, so it is important to discuss with your doctor all medications the patient is taking to treat comorbidities before starting a course. In fact, this is one of the main obstacles to the widespread application of the drug among patients with a high risk of coronavirus infection severe course, since the majority of them have more than one chronic disease and take from 5 to 10 different drugs.

Paxlovid should not be used in people with severely impaired kidney or liver function. In addition, Paxlovid may contribute to acquisition of resistance to HIV therapy. Therefore, for COVID-19 treatment in patients with HIV, the doctor may choose a different strategy.

So far, there is no reliable data on how Paxlovid affects on pregnancy course in humans. However, a study published in peer-reviewed scientific journal Reproductive Toxicology indicates that taking Paxlovid at a concentration corresponding to therapeutic one for humans does not affect the fertility of males and females, as well as pregnancy development in laboratory rats and rabbits. This gives hope that after appropriate clinical trials, the drug will be allowed to be used for  COVID-19 treatment in pregnant women.

There are no reliable data about drug’s components presence in woman breast milk and their effect on infants. The manufacturer does not recommend to use Paxlovid for treatment of nursing mothers.

Pfizer prohibits pediatricians from prescribing Paxlovid to patients with COVID-19 who are under the age of 12 or who weigh less than 40 kg. This is because scientists have not yet tested its safety and effectiveness in this age group.

In January 2022, Pfizer released the results of three independent clinical trials proving the drug’s effectiveness against Omicron. Nature experts suggest that Paxlovid will also be effective against future variants of SARS-COV-2, because mutations usually concern the part of the virus genome that is responsible for spike protein, and not for protease that is the target of the drug.

Paxlovid’s main competitor is Remdesavir. This is also a direct antiviral agent, an inhibitor of SARS-COV-2 proteases, but the agent is administered by injection. Paxlovid is the first drug in form of pills in its class, which is a great advantage. It can be taken on an outpatient basis, which significantly improves compliance and access to medical care for patients.