Preliminary data of Pfizer's Covid-19 pill Paxlovid 'sounds promising' but more data needed: NCID

SINGAPORE - The preliminary data for Pfizer's new antiviral pill "sounds promising", said the National Centre for Infectious Diseases (NCID), adding that it is waiting for further data to be released before considering the drug for use in Covid-19 patients here.

The preliminary data has shown the drug was able to cut by 89 per cent the chances of hospitalisation or death in adults at risk of developing severe disease, said Pfizer on Nov 5.

They include those who had mild-to-moderate symptoms within a five-day period, and are at risk of developing severe illness such as chronic lung disease, high blood pressure or diabetes.

Pfizer said in response to queries from The Straits Times that it plans to submit its interim trial results for the pill to be authorised for emergency use by the US Food and Drug Administration "as soon as possible".

This will be followed by submissions in other markets, though Pfizer added that it "cannot speculate on timelines".

The treatment, known as Paxlovid, combines Pfizer's new drug with an older antiviral known as ritonavir.

The drug is designed to block the activity of the Sars-CoV-2 viral 3CL protease, an enzyme that releases viral proteins for the coronavirus to replicate.

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As the structure of the enzyme is highly conserved in the coronavirus family, Pfizer said it believes the efficacy of the pill will not very likely be negatively impacted by emerging variants.

In the lab, the pill has demonstrated potent antiviral activity against circulating variants of concerns, as well as other known coronaviruses, suggesting its potential as a therapeutic for multiple types of coronavirus infections, it added.

A low dose of ritonavir helps to slow down the metabolism or breakdown of the pill so that it can remain active in the body for a longer period, said Pfizer.

Pfizer's Paxlovid treatment comes on the back of Merck and Ridgeback Therapeutics' antiviral pill, Molnupiravir, which is able to halve the chance of hospitalisation and death for those at risk of severe disease.

Singapore has recently inked a supply and purchase agreement for the drug with Merck, which is known as MSD outside the US and Canada.

The drug will be available for use if MSD submits its data to the Health Sciences Authority (HSA) and obtains authorisation for its use in Singapore. The timeline for approval depends on the company's submission of data to HSA.

Dr Shawn Vasoo, clinical director of NCID, told ST that it is important to compare the details of both trials to determine which one would be considered more effective.

"In any case, an effective, oral antiviral in early Covid-19 particularly for high-risk individuals would be a welcome addition to the available treatment options," he said.

Another drug that was recently in the public limelight is an antidepressant known as fluvoxamine, which has been touted to reduce severe Covid-19.

Dr Vasoo said fluvoxamine is hypothesised to have an effect on Covid-19 by reducing its inflammatory cascade, and possibly has some anti-clotting effects.

However, he noted that further studies are needed as it is "not so clear at this point" if there is a definite role for the re-purposed drug as yet.

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It is hypothesised that fluvoxamine works by activating the S1R - a protein which regulates the production of cytokines that control immune and inflammation responses. This is said to decrease the damage induced by cytokines during Covid-19 infection.

Two trials have been conducted so far - a large one in Brazil involving around 1,500 participants, and a smaller-scale study from St. Louis, Missouri, in the US.

Dr Vasoo noted that the Brazil trial looked at the number of patients who needed to be observed in the Emergency Department for more than six hours or who were hospitalised for Covid-19 for up to 28 days after enrolment.

"These are 'softer' (not as definite) end-points to evaluate a drug's efficacy, when compared to a 'harder' end point such as death or 28-day hospitalisation," said Dr Vasoo.

He also said the Brazilian study did not find differences in viral clearance, hospitalisation or death in their analysis.

"In addition, the study from St Louis was a preliminary study limited by a small sample size and a short follow-up of only 15 days. Hence, these results for fluvoxamine may not be considered definitive and further data is needed," he added.

Current treatment options for Covid-19 consist of the following: steroids like dexamethasone, antivirals such as remdisivir, antibody drugs such as sotrovimab and regeneron and tocilizumb, as well as anti-inflammatory drugs like baricitinib.