PAXLOVID™ (PF-07321332; ritonavir)

Paxlovid is a novel, COVID-19, oral, antiviral candidate. PAXLOVID™ is a SARS-CoV-2-3CL protease (an enzyme that the coronavirus needs to replicate) inhibitor, which originated in Pfizer’s laboratories. It may have efficacy as a prophylaxis and/or outpatient treatment. Co-administration with a low dose of ritonavir helps slow the metabolism, or breakdown, of PF-07321332 in order for it to remain active in the body for longer periods of time at higher concentrations to help combat the virus.


  • 22 December 2021: EUA1) in the USA for patients 12 years of age and older weighing at least 40 kg with mild-to-moderate COVID-19, and who are at high risk for progression to severe COVID-19, including hospitalization or death.
  • 31 December 2021: UK MHRA grants approval2) to Pfizer’s oral antiviral for Covid-19 for mild to moderate COVID-19 infected patients who are at an increased risk of developing severe disease.
  • 16 January 2022: Canada’s health regulator has approved Paxlovid.3)

Clinical Trials

The Phase 2/3 EPIC-HR (Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients) study began enrollment in July 2021.
The Phase 2/3 EPIC-SR (Evaluation of Protease Inhibition for COVID-19 in Standard-Risk Patients) and EPIC-PEP (Evaluation of Protease Inhibition for COVID-19 in Post-Exposure Prophylaxis) studies, began in August and September 2021 respectively.

NCT04960202 EPIC-HR: Study of Oral PF-07321332/Ritonavir Compared With Placebo in Nonhospitalized High Risk Adults With COVID-19
NCT05047601 A Post-Exposure Prophylaxis Study of PF-07321332/Ritonavir in Adult Household Contacts of an Individual With Symptomatic COVID-19
NCT05011513 Evaluation of Protease Inhibition for COVID-19 in Standard-Risk Patients (EPIC-SR)
NCT05032950 Drug-Drug Interaction Study to Estimate the Effect of PF-07321332/Ritonavir and Ritonavir on Midazolam in Healthy Participants
NCT04962022 Drug-Drug Interaction Study Assessing Effect of Itraconazole on PF-07321332/Ritonavir in Healthy Participants
NCT04909853 Renal Impairment Study of PF-07321332 Boosted With Ritonavir in Adult Participants With Renal Impairment and in Healthy Participants With Normal Renal Function
NCT05005312 Study to Estimate the Effects of Hepatic Impairment on the Pharmacokinetics (PK) of PF-07321332
NCT05129475 Food Effect Study to Evaluate the Effect of High-Fat Meal on the Relative Bioavailability of PF-07321332 Boosted With Ritonavir in Healthy Adult Participants
NCT05064800 PF-07321332/Ritonavir and Ritonavir on Dabigatran Study in Healthy Participants

Press Releases

On Friday, November 5, 2021, Pfizer issued a stunningly optimistic press release for a new drug, stating “overwhelming efficacy” and a risk reduction of 89% for hospitalization and death from COVID-19.4) The press release claimed that after 28 days there were 0 deaths in the treatment arm and 10 in the placebo arm, with 41 vs. 6 hospitalizations.

Adverse Events

Adverse events in the PAXLOVID group (≥1%) that occurred at a greater frequency (≥5 subject difference) than in the placebo group were dysgeusia (6% and <1%, respectively), diarrhea (3% and 2%), and hypertension (1% and <1%), and myalgia (1% and <1%). The proportions of subjects who discontinued treatment due to an adverse event were 2% in the PAXLOVID group and 4% in the placebo group.

The National Post reported that a component of the drug can “interact dangerously with a slew of commonly used medications, pumping up the potency of blood thinners, heart-arrhythmia therapies, epilepsy drugs and others. And the patients targeted for its use – those most at risk of serious COVID disease because of age and other health issues – are also the people most likely to be taking those 'contraindicated' medications.”5)

Articles in Medical Journals

In the News


Country Doses Secured Price Date
Canada 1,000,000 ??? 3 Dec 2021
USA 10,000,000 $5.29 billion 18 Nov 2021
UK 250,000 ??? Nov 2021
Israel tens of thousands ??? 15 Nov 2021
USA 10,000,000 ??? 04 Jan 2022

An Alternate View

Note that there is no peer-reviewed article available describing the clinical trial and its results, nor is there even an FDA Briefing Document that I (JMG) can find for review. Literally everything we know about this medication so far has come from Pfizer, largely thru press releases and other communications.

For a somewhat jaundiced view of this medication see

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