WASHINGTON D.C. (ENDPOINTS News) – The FDA on Thursday authorized another new pill to treat the Omicron variant, this time from Merck.

The FDA decision follows upon a decision Wednesday authorizing Pfizer’s Paxlovid oral treatment, which the company said had proved to reduce the relative risk of hospitalization or death by 89% (within three days of symptom onset) and 88% (within five days of symptom onset) compared to placebo in a trial of more than 2,000 people.

Merck’s pill, monulpiravir, saw its efficacy plummet between interim and final analyses in its pivotal trial — from a 50% relative reduction in hospitalizations and deaths at the interim to just 30% in the final results — meaning that more doctors will likely rely on the Pfizer pill. There are also questions about how Merck’s pill works, which led France’s experts to reject it.

While Pfizer’s antiviral may prove to be more effective, and Merck’s pill has left some scientists questioning the dangers behind its mechanism of action, molnupiravir will be another weapon in the armamentarium of Covid-19 treatments for the US in a time of need, as two mAb treatments from Regeneron and Eli Lilly are no longer effective against Omicron, and as supplies of a third mAb from Vir/GlaxoSmithKline are very limited.

Merck has also reached a deal for the worldwide distribution of monulpiravir at reduced prices, through the Medicines Patent Pool, while Pfizer has said it will offer it’s pill to low- and middle-income countries at reduced prices.

Pfizer Says New Anti-Viral Drug Combination Cuts Risks Of Serious COVID-19 By 89% 

Supplies of Merck pill more immediately available

In the US, as well, supplies of the Merck pill will not be as limited, as the US may have about 400,000 courses of Merck’s pill available in the next few days, and by the end of January, the US government expects to have about 3 million courses of Merck’s pill, which is the entire order that the US made.

The concern with Merck’s pill is that it works by inhibiting SARS-CoV-2 replication through viral mutagenesis, and some scientists have raised serious reservations about that MOA.

The FDA’s Antimicrobial Drugs Advisory Committee narrowly voted 13-10 last month in favor of the pill’s benefits outweighing the risks for adults within 5 days of developing Covid symptoms.

“Committee members who voted ‘No’ cited the following as reasons for concluding that the overall benefit-risk ratio was unfavorable: 1) a high number-needed-to-treat compared with placebo, 2) unclear efficacy against the Delta variant, 3) potential to drive viral mutations, and 4) mutagenicity risks,” according to a summary of the meeting.

Merck has to provide reports to the FDA on a monthly basis summarizing any findings as a result of its monitoring activities of genomic database(s) for the emergence of global viral variants.

As part of Thursday’s authorization, FDA made clear that it should be provided to those “for whom alternative COVID-19 treatment options authorized by FDA are not accessible or clinically appropriate,” meaning that if Pfizer’s pill is available, that might be a better option.

Scientists still see wider preference for Pfizer pill

“I don’t think you would find anyone who would prefer the Merck pill to the Pfizer pill, given the data evident so far,” Walid Gellad, a professor of medicine at the University of Pittsburgh, told Endpoints News previously.

As part of the EUA, the FDA said Merck has to “conduct a thorough investigation into the differences in efficacy observed in the first and second half” of its pivotal trial. Panelists at the adcomm last month centered their questioning on the cause of this drop-off in preventing hospitalizations and deaths, from 50% to 30% between interim and final results. Merck and the FDA offered few specifics at the meeting on why the efficacy declined.

Unlike the Pfizer pill, the FDA also warned Thursday that molnupiravir is not recommended for use during pregnancy, as based on findings from animal reproduction studies, molnupiravir may cause fetal harm.

Merck must maintain a pregnancy surveillance program to collect information on individuals who are exposed to molnupiravir during pregnancy. FDA also said that sexually active individuals with partners of childbearing potential are advised to use contraception during molnupiravir treatment and for at least three months after the last dose.

Molnupiravir is also not authorized for use in patients who are less than 18 years of age, or for use for longer than 5 consecutive days. A course of treatment is administered as four 200 milligram capsules taken orally every 12 hours for five days, for a total of 40 capsules.

Reprinted with permission from ENDPOINTS News: FDA Authorizes New Merck COVID-19 Pill & FDA authorizes the first at-home pills from Pfrizer to treat COVID-19.  @ZacharyBrennan is a senior editor covering the FDA and regulatory policy.

Image Credits: Pfizer .