Covid pills: How the Pfizer and Merck oral treatments work

Australia’s first oral treatments for Covid-19 could be a game-changer in the battle against Covid-19. Here’s what we know.

Australia’s medicines watchdog has given provisional approval to two oral Covid-19 treatments.

Paxlovid, developed by Pfizer and Lagevrio, developed by Merck Sharp & Dohme, are the first Covid pills to be approved in Australia.

Here’s what we know:

WHO CAN TAKE THE PILLS?

Both pills have been given the green light for the treatment of adults with Covid-19 who do not require oxygen and who are at increased risk of hospitalisation or death.

“It’s not for everybody, it’s designed for those who are most at risk, so particular the elderly,” Health Minister Greg Hunt told the Seven Network.

Significantly, neither product is intended to be used as a substitute for vaccination against Covid-19.

WHEN SHOULD THE PILLS BE TAKEN?

As soon as possible after a Covid-19 diagnosis and within five days of the start of symptoms. Lagevrio is available as capsules, while Paxlovid comprises separate tablets of nirmatrelvir and ritonavir.

In both cases, the medicines are taken twice a day for five days.

The making of Paxlovid at a laboratory in Freiburg, Germany. Picture: Handout/ Pfizer/ AFP.

HOW DO THE PILLS WORK?

Lagevrio deters replication of the SARS-CoV-2 virus.

In Paxlovid, the nirmatrelvir component blocks the activity of a protease enzyme that the coronavirus needs in order to replicate. Nirmatrelvir is administered in combination with low-dose ritonavir to maintain plasma levels of nirmatrelvir for the duration of the treatment.

Pfizer lab tests found the drug works against Covid-19, including the Omicron variant, by reducing risk of hospitalisation or death by nearly 90 per cent compared to placebo for high-risk patients when treated within five days of symptom onset.

“These data suggest that our oral Covid-19 therapy can be an important and effective tool in our continued battle against this devastating virus and current variants of concern, including the highly transmissible Omicron. We will continue to monitor the treatment’s activity in real-world settings and believe that these in vitro findings will continue to be validated,” the company’s chief scientific officer Mikael Dolsten said.

CAUTIONS

The use of Lagevrio is not recommended in pregnancy and breastfeeding. It is recommended that sexually active women of child-bearing potential use contraception and men also use contraception during and three months after treatment with Lagevrio.

The use of Paxlovid is also not recommended in pregnancy or breastfeeding, and in women of child-bearing potential. It is recommended that sexually active women of child-bearing potential use contraception.

Paxlovid must also not be used with a number of other commonly used medicines, either because for some medicines this may lead to potentially harmful increases in their blood levels, or in the case of some other medicines they may reduce the activity of Paxlovid. The list of medicines that must not be used with Paxlovid is included in the Product Information. Paxlovid must also not be used in patients with severely reduced kidney or liver function.

A Covid-19 patient lies in bed in an ICU ward. The oral pills are designed to prevent hospitalisation and death. Picture: AFP

WHEN IS IT ARRIVING

Health Minister Greg Hunt told ABC Radio the products were expected to arrive in coming weeks, after the government secured 500,000 courses of Paxlovid and 300,000 courses of Lagevrio. 

“They will help people who are at increase risk of going from mild to moderate and deemed by medical professionals to have the risk of progression of more serious conditions,” Mr Hunt said.

“They are expected to arrive in the coming weeks.

“(They) will build on what we’re already doing through the intravenous or hospital treatments.”

DO OTHER COUNTRIES USE THE PILLS?

Paxlovid has received conditional marketing authorisation from the UK Medicines and Healthcare products Regulatory Agency and emergency use authorisation from the US Food and Drug Administration, it was also authorised by Health Canada earlier this week.

HOW SAFE ARE THE PILLS?

The TGA says Australians can be confident that its review process of Paxlovid was rigorous. The decision to provisionally approve the vaccine was also informed by expert advice from the Advisory Committee on Medicines (ACM), an independent committee with expertise in scientific, medical and clinical fields including consumer representation.

Originally published as Covid pills: How the Pfizer and Merck oral treatments work