Covid-19: The giant Pfizer tests a pill against severe forms

In recent weeks, Pfizer has launched a clinical trial to test the effectiveness of an antiviral pill against Covid-19. The active substance, a protease inhibitor, is already used to fight against other viruses.

Pfizer’s vaccine was the first to obtain emergency clearance and be administered to prevent severe forms of Covid-19. The pharmaceutical company is working in parallel on another track to treat the disease, an oral drug that contains an antiviral molecule. On March 23, Pfizer announced the start of a phase I clinical trial to assess the safety and tolerance of patients to this drug, called PF-07321332.

Act on the enzymes of the coronavirus

Behind this name hides a protease inhibitor, that is to say a molecule that prevents the action of this enzyme. However, it is essential for the replication of the coronavirus. Indeed, the translation of the virus genome results in the production of two polyproteins, among others. These two polyproteins must be broken to release each protein they contain, among them there are in particular the proteins which constitute the viral capsid. Without the splitting of the polyprotein, the virus cannot complete its cycle and this event is mediated by a protease. However, it is precisely this protease that the PF-07321332 molecule inhibits. This strategy is already being used to combat other viruses, such as HIV.

“We designed PF-07321332 as a potential oral therapy that could be prescribed at the first sign of infection, without requiring patients to be hospitalized or in intensive care. At the same time, Pfizer’s other intravenous antiviral is a new treatment option for inpatients. Together, the two have the potential to create an end-to-end treatment paradigm that complements vaccination in cases where disease persists, ”says Mikael Dolsten, research director at Pfizer.

Indeed, Pfizer is testing a second antiviral which will be more intended for hospitalized patients since it is injected intravenously, PF-07304814. It is also being tested in a phase I clinical trial.



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