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 Here is an explanation of the differences in the two pills.
Which of the new pills works better?
Trial data provided by the two companies suggest that Pfizer has the
more effective pill.
Pfizer in December said final trial results showed that its
treatment reduced the chance of hospitalization or death by 89% in
COVID-19 patients at risk of severe illness given the treatment
within three days of the onset of symptoms, and by 88% when given
within five days of onset.
Merck in November said its full trial results showed that
molnupiravir lowered the chance of hospitalization or death by about
30% in patients at risk of severe COVID who were given the treatment
within five days of developing symptoms.
An earlier, interim look at Merck's trial on Oct. 1
https://www.reuters.com/business/
healthcare-pharmaceuticals/mercks-covid-19-pill-cuts-risk-death-hospitalization-by-50-study-2021-10-01
had suggested that molnupiravir halved the risk of hospitalization
or death. Merck did not provide figures regarding patients getting
the pill within three days of onset.
Pfizer's two-drug regimen is being sold under the brand name
Paxlovid. Merck's drug has the brand name Lagevrio.
Why are these drugs important?
While a number of vaccines are available worldwide to help prevent
infection and serious illness, including one made by Pfizer, there
are limited treatment options for people infected with COVID-19.
Currently, COVID-19 patients who are not sick enough to be
hospitalized but are at risk of serious illness can be treated with
antibody drugs, though they have to be given intravenously at
hospitals or infusion centers.
Antibodies developed early in the pandemic have not held up against
the now dominant Omicron coronavirus variant. Sotrovimab, from
GlaxoSmithKline and Vir Biotechnology, which in trials reduced the
risk of hospitalization and death by 85%, has shown to be effective
against the highly-transmissable variant.
Gilead Sciences Inc's intravenous antiviral drug remdesivir, sold as
Veklury, was recently given emergency approval by U.S. regulators as
a three-day infusion for at-risk COVID patients after it was shown
to reduce their risk of hospitalization by 87%.
How do they work?
Both oral regimens are given for five days. Pfizer's regimen is
three pills in the morning and three pills at night. Merck's drug is
taken as four pills in the morning and four at night.
Pfizer's drug is part of a class known as protease inhibitors
designed to block an enzyme that the coronavirus needs to multiply.
It is given in combination with ritonavir, an older antiviral that
boosts the activity of protease inhibitors but can cause
gastrointestinal side effects and interfere with certain other
medications.
Merck's pill, developed with Ridgeback Biotherapeutics, is a
nucleoside analogue with a mechanism of action that aims to
introduce errors into the genetic code of the virus.
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 Both companies have said laboratory studies show
that their pills are active against coronavirus
infections caused by the Omicron variant.
What do we know about safety?
Both companies have released only limited data
on the treatments, but expressed confidence in
their safety.
Pfizer said about 20% of patients who received
either the pill or a placebo in trials
experienced adverse events, mostly mild. Serious
side effects were reported by 1.7% of patients
receiving the drug and 6.6% of placebo patients.
Since the ritonavir component of Paxlovid can
interfere with other medications, physicians
emphasize that patients need to share an
accurate list of any other drugs they are taking
before being prescribed the Pfizer drug.
Merck said 12% of patients receiving its drug
and 11% of placebo patients experienced
drug-related adverse events.
Drugs in the same class as Merck's pill have
been linked to birth defects in animal studies.
Merck has said similar studies of molnupiravir -
for longer and at higher doses than used in
humans - show that it does not cause birth
defects or cancer.
Molnupiravir is not authorized for U.S. patients
younger than 18 years of age because it could
affect bone and cartilage growth. It is also not
recommended for use during pregnancy.
The U.S. Food and Drug Administration advises
that both men and women of child-bearing age be
on reliable birth control while taking the Merck
drug, and that it cannot be used by pregnant
women.
What do we know about supplies?
Pfizer and Merck have said they are making
efforts to expand global access to the drugs,
including allowing generic drugmakers to sell
lower-cost versions in low-income countries.
Pfizer has said it expects to have capacity to
produce up to 120 million courses of its therapy
this year.
Merck has said it could produce at least 20
million courses of its drug this year.
Which costs more?
The U.S. government provides vaccines and
treatments for COVID-19 for free to U.S.
residents. Countries around the world are
negotiating prices with Pfizer and Merck.
The United States is paying around $530 for each
course of Paxlovid and $700 for each course of
molnupiravir.
(Reporting By Deena Beasley; Editing by Bill
Berkrot)
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