On Wednesday afternoon, the Food and Drug authorised the first antiviral pill for treating covid-19: the Pfizer-developed treatment Paxlovid. In clinical trials, Paxlovid was found to reduce the likelihood of severe illness from covid-19 among high-risk patients soon after infection by nearly 90%.
Paxlovid is a two-drug combination of nirmatrelvir, an antiviral newly developed by Pfizer designed to stop the coronavirus from replicating inside cells, and ritonavir, a long-existing antiviral used to treat HIV (ritonavir is thought to extend the longevity of nirmatrelvir in the body). It’s taken as three tablets twice a day, for no longer than five days, and is meant to be prescribed as soon as possible following a positive covid-19 test and within five days of symptoms starting. It will be recommended for people over 12 who have mild to moderate covid-19 but also have risk factors that predispose them to severe covid-19.
In the pivotal clinical research examined by the FDA, which involved over 2,000 people, high-risk patients with mild to moderate covid-19 given Paxlovid were 88% less likely to be hospitalized from covid-19 or die from any cause in the following month than those given a placebo. Overall, around 0.8% of patients on Paxlovid died or were hospitalized by covid-19, compared to 6% of the control group.
Since early on in the pandemic, scientists have been looking for treatments that can help treat or prevent the worst outcomes of covid-19. A few options have panned out, such as monoclonal antibodies, but many haven’t — and even these antibodies require dedicated infusion centres and are difficult to scale up. For this reason, many experts are understandably excited about the potential of Paxlovid.
“Today’s authorization introduces the first treatment for covid-19 that is in the form of a pill that is taken orally — a major step forward in the fight against this global pandemic,” said Patrizia Cavazzoni, M.D., director of the FDA’s Centre for Drug Evaluation and Research, in the FDA’s announcement of their emergency use authorization. “This authorization provides a new tool to combat covid-19 at a crucial time in the pandemic as new variants emerge and promises to make antiviral treatment more accessible to patients who are at high risk for progression to severe covid-19.”
Some monoclonal antibodies have now fallen out of favour, with early data showing that they aren’t as effective against the Omicron variant as before (Omicron’s mutations are thought to make it especially good at evading antibodies trained to recognise the original coronavirus). However, Pfizer claims their data shows that Paxlovid should remain effective against Omicron and other variants.
Paxlovid isn’t likely to be the only antiviral soon available for covid-19. Merck’s treatment molnupiravir is also expected to be authorised by the FDA within days, though the drug doesn’t have as impressive results as Paxlovid. In clinical trials, molnupiravir was found to reduce the risk of covid-related hospitalisation and death by 30% — down from the projected 50% efficacy the company claimed earlier citing their interim data. There are also some added safety concerns about molnupiravir, which relies on causing mutations within the coronavirus using a mechanism that could theoretically affect human cells as well (in studies, Paxlovid showed no such potential risk). These risks are not definite, but they may limit the application of molnupiravir, such as avoiding its use in people considering pregnancy.
Another problem that could affect the success of both treatments is whether Americans will be able to access them. The Biden Administration has secured the delivery of 10 million doses of Paxlovid and has pledged to make them easily available and free.