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The role of antiviral treatment in the COVID-19 pandemic

The role of antiviral treatment in the COVID-19 pandemic

On December 22, 2021, the U.S. Food and Drug Administration (FDA) issued an emergency clearance for Pfizer’s COVID-19 antiviral drug, Paxlovíd. Research results released by the manufacturer indicate that the drug reduces the risk of hospitalization or death for high-risk patients by 88%, compared to the placebo, when given within 5 days of the onset of symptoms. A Second Oral Antiviral, Merck Sharp & Dohme’s (MSD) molnupiravir, received FDA approval on December 23. In a Phase 3 study of 1433 patients with mild to moderate COVID-19 and at least one risk factor for serious disease, treatment with molnupiravir within 3 days of symptom onset reduced the risk of hospitalization or death by 30%, compared to the placebo.
Remdesivir has already been shown to shorten recovery times in hospitalized patients with COVID-19. Process results published last month it appeared that it is also effective earlier in the course of the disease. Treatment with remdesivir within 7 days of the onset of symptoms reduced the risk of hospitalization or death by 87%, compared with placebo, for non-hospitalized patients with COVID-19 who were at high risk for serious illness. But the drug has to be administered intravenously, which drastically limits its usefulness, especially in patients who would otherwise be isolated at home.

Pfizer and MSD have both entered into agreements with the Medicines Patent Pool (MPP), giving dozens of low- and middle-income countries around the world access to Paxlovid and molnupiravir. MSD has separately signed licensing agreements with several manufacturers of generic drugs. Charles Gore, executive director of the MPP, expects the generic version of molnupiravir to initially sell for about US$20 in the 105 countries included in the deal with the MPP.

“The oral antivirals don’t have the complications of the monoclonal antibodies, which have to be given in the hospital, and they’re a lot cheaper,” Gore said. The Lancet Respiratory Medicine. “They are very suitable for low- and middle-income countries.” Predicting demand will be tricky, but Gore believes the MPP has licensed enough suppliers to minimize the potential for shortages.

Molnupiravir is easy to manufacture and so is likely to be the most widely available antiviral agent for COVID-19 for the time being. Paxlovid is a more complicated product. It is a combination of two drugs: ritonavir plus the new protease inhibitor PF-07321332. The two drugs work in different ways. Molnupiravir causes an accumulation of errors in the replicating virus, until the virus can no longer survive. Paxlovid blocks a protease necessary for the replication process. Paxlovid’s results are more promising than those for molnupiravir, although they have yet to be published in the scientific press. France responded to the publication of the full results of the molnupiravir study by canceling an order for 50,000 doses of the antiviral – the interim results had suggested that molnupiravir cut the risk of hospitalization in half.

“There’s a good chance we can cut the cost of molnupiravir to $10 per course; that’s a great price for a 30% reduction in hospitalizations,” Gore said. The US government has agreed to pay about $530 per course of Paxlovid and $700 per course of molnupiravir.On January 4, 2022, the Indian pharmaceutical company Dr. Reddy’s Laboratories announced that it would sell a course of its version of molnupiravir for 1,400 rupees (US$18.85).

Charlotte Summers, a professor of intensive care at the University of Cambridge (Cambridge, UK), welcomed the arrival of oral antivirals. But she pointed out that there are still questions about the role they are likely to play in fighting the pandemic. The Phase 3 studies for both molnupiravir and Paxlovid recruited unvaccinated individuals at high risk of hospitalization for COVID-19. “We don’t have many of these people in the UK anymore,” Summers noted. “We don’t know what the outcome of these drugs will be in vaccinated populations, or whether they will provide benefits to patients who are not at high risk for serious disease.” There are many unvaccinated people in low- and middle-income countries. But for antivirals to be effective, treatment must be started quickly. This will be problematic in places with limited access to diagnostics.

In addition, Paxlovid is associated with several drug interactions, which could complicate its use in the community. There are concerns that molnupiravir could potentially affect bone and cartilage growth; the FDA authorization does not apply to people under the age of 18.

The PANORAMIC study will look at the effectiveness of several COVID-19 antivirals in high-risk patients in the UK. The majority of participants are likely to be vaccinated. A sub-study within the trial will investigate whether the antivirals prevent the transmission of SARS-CoV-2. The researchers began recruiting for a study looking at the effectiveness of early treatment with molnupiravir last month. There are no clinical studies combining molnupiravir and Paxlovid yet. “We really need to look at combination therapies,” Summers said. “It’s hard enough to come up with effective antivirals; we must do everything we can to prevent the development of resistance.”