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PAXLOVID Oral Antiviral (Nirmatrelvir)

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August 13, 2022
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PAXLOVID™ Oral Antiviral (nirmatrelvir, ritonavir) Description For 2022

Pfizer Inc. Paxlovid™ (nirmatrelvir, BexovidritonavirPF-07321332) is an oral antiviral therapeutic targeting the SARS-CoV-2 beta coronavirus to prevent COVID-19. Paxlovid is packaged with nirmatrelvir and ritonavir, a strong cytochrome P450 (CYP) 3A4 inhibitor. Nirmatrelvir, a novel main protease (Mpro) inhibitor originating in Pfizer's laboratories, is specifically designed to block the activity of the SARS-CoV-2 Mpro, an enzyme the coronavirus needs to replicate. It is an analog of GC373, where the aldehyde covalent cysteine acceptor replaced a nitrile. 

Paxlovid works intracellularly by binding to the highly conserved main protease of the SARS-CoV-2. By inhibiting the main protease, Paxlovid inhibits viral replication at a stage known as proteolysis, which occurs before viral RNA replication. Protease inhibitors bind to a viral enzyme, preventing the virus from replicating in the cell. Protease inhibitors effectively treat other viral pathogens, such as HIV and hepatitis C virus. 

Pfizer developed PF-07321332 by modifying PF-07304814 (Lufotrelvir), a covalent inhibitor. PF-07321332 is also a covalent inhibitor, but its warhead is a phosphate prodrug, a hydroxyketone. Paxlovid is co-administration with a low dose of ritonavir, a strong cytochrome P450 (CYP) 3A inhibitor, to slow the metabolism or breakdown of Paxlovid and to remain active in the body for more extended periods at higher concentrations to help combat the virus. In preclinical studies, PF-07321332 did not demonstrate evidence of mutagenic DNA interactions. However, Paxlovid has complex drug-drug interactions, primarily due to the ritonavir component.

The U.S. NIH stated that therapeutic options are now available for treating nonhospitalized adults with mild to moderate COVID-19. Paxlovid became the first orally administered coronavirus-specific investigational protease inhibitor authorized for certain adults and children by the U.S. FDA on Dec. 22, 2021. Then on Jan. 28, 2022, the European Medicines Agency (EMA) and European Commission granted Pfizer Europe MA EEIG marketing authorization EMEA/H/C/005973 for adults. And effective from Feb. 10, 2022, Paxlovid was added as a first-line treatment option for patients with hospital-onset COVID infection in the U.K. Paxlovid treatment should be initiated within five days of disease symptom onset, says the U.S. NIH.

On Jun. 14, 2022, Pfizer shared data from the Phase 2/3 EPIC-SR study evaluating the use of PAXLOVID in patients who are at standard risk for developing severe COVID-19. An updated analysis showed a non-significant 51% relative risk reduction (treatment arm: 5/576; placebo: 10/569). A sub-group analysis of 721 vaccinated adults with at least one risk factor for progression to severe COVID-19 showed a non-significant 57% relative risk reduction in hospitalization or death (treatment arm: 3/361; placebo: 7/360).

The WHO made a strong recommendation on Apr. 22, 2022, for Paxlovid, for mild and moderate COVID-19 patients at the highest risk of hospital admission, calling it the best therapeutic choice for high-risk patients to date.

Pfizer confirmed on Apr. 29, 2022, top-line results from the Phase 2/3 EPIC-PEP study evaluating PAXLOVID for post-exposure prophylactic use. In this trial, compared to placebo, Pfizer observed risk reductions of 32% and 37% in adults who received PAXLOVID for five and ten days, respectively, to prevent infection. However, these results were not statistically significant. As such, the primary endpoint of reducing the risk of confirmed and symptomatic COVID-19 infection in adults who had been exposed to the virus through household contact was not met. 

The May 2022 Institute for Clinical and Economic Review (ICER) determined that Pfizer's Paxlovid earned all 13 panelists' positive votes. Dr. John Farley, director of the Office of Infectious Diseases, provided information according to the National Institutes of Health COVID Treatment Guidelines on May 4, 2022: 'there is no evidence of benefit at this time for a longer course of treatment (e.g., 10 days rather than the 5 days recommended) or repeating a treatment course of Paxlovid in patients with recurrent COVID-19 symptoms following completion of a treatment course.' A large real-world study conducted in Israel reported on Jun. 2, 2022, 'The magnitude of risk reduction was larger in the EPIC-HR trial (88%) than in the current study (46%). The lower risk reduction observed in the real world might be explained by several differences between the studies, including those related to the coronavirus.'

As of the end of Jun. 2022, Pfizer had shipped more than 12 million Paxlovid courses to nearly 40 countries. Since Dec. 2021, the U.S. government distributed about 6,238,027 Paxlovid treatments in the USA. On July 6, 2022, the FDA published updated: FAQs on the Authorization (including state-based pharmacists in the USA) for Paxlovid use.

Please see the EUA Prescribing Information available at fda.gov and COVID19oralRx.com. Chemical Formula: C23H32F3N5O4; DrugBank Accession Number DB16691; CAS Number 2628280-40-8; PubChem CID 155903259; Molecular Weight: 499.5. Contact [email protected].​gov with any questions. To learn more, please visit New York-based Pfizer Inc. at www.Pfizer.com. (NYSE: PFE).

PAXLOVID Omicron BA.x Sublineages

Current coronavirus variants can be resistant to treatments and vaccines that work by binding to the spike protein found on the surface of the SARS-CoV-2 virus. A non-peer-reviewed study published on July 4, 2022, identified several mutations such as Y54C, G138S, L167F, Q192R, A194S, and F305L in the SARS-CoV-2 3CLpro that confer resistance to the protease inhibitor nirmatrelvir.

As of Aug. 4, 2022, the U.S. NIH OpenData Portal reports nirmatrelvir (Paxlovid's main ingredient) excluding ritonavir, in vitro Therapeutic Activity against SARS-CoV-2 coronavirus variants, as does the U.K.'s CoVariants. And the EMA published a Paxlovid Assentment Report (EMA/95110/2022) on Jan. 27, 2022. As does the GISAID Initiative's COVIDcg.org.

A recent non-peer-reviewed preprint study published by virology researchers at Austria's Medical University of Innsbruck on July 4, 2022, concluded 'Mutations of the main protease of SARS-CoV-2 result in resistance against licensed drugs such as Paxlovid (nirmatrelvir / ritonavir).

Pfizer Inc. shared results from multiple studies demonstrating on Jan. 18, 2022, that the in vitro efficacy of nirmatrelvir, the active main protease (Mpro) inhibitor of PAXLOVID, is maintained against the SARS-CoV-2 variant Omicron. Pfizer also announced on Dec. 14, 2021, that recent in vitro data confirm that nirmatrelvir is a potent inhibitor of the Omicron 3CL protease, which, combined with existing in vitro antiviral and protease inhibition data from other Variants of Concern (VoC), including Delta, indicates that PAXLOVID will retain robust antiviral activity against current VoCs as well as other coronaviruses.

PAXLOVID Rebound

The peer-review journal Nature published - COVID rebound is surprisingly common — even without Paxlovidon on Aug. 12, 2022. 'Early (non-peer-reviewed) data hint that the rebound is even more pronounced after antiviral treatment.'

The U.S. CDC issued this Health Alert Network Health Advisory (CDCHAN-0467) on May 24, 2022, updating healthcare providers, public health departments, and the public on the potential for recurrence of COVID-19 or “COVID-19 rebound.”

Pfizer Inc. confirmed on Jun. 30, 2022, 'Data which show that the frequency of return of detectable nasal viral RNA following PAXLOVID treatment was low and generally similar among PAXLOVID and placebo recipients.' A non-peer-reviewed study conducted by researchers published by US-based researchers on June 28, 2022, identified several drug-resistant hot spots that warrant close monitoring for possible clinical evidence of Paxlovid resistance. About 11 naturally occurring mutations of Mpro, the target of Paxlovid, could confer resistance. Naturally occurring SARS-CoV-2 Mpro polymorphisms could potentially affect the efficacy of Paxlovid, and continuous prescription of Paxlovid might increase the frequency of these pre-existing drug resistance mutants.

COVID-19–related hospital admissions and emergency department (ED) encounters occurring 5–15 days after Paxlovid treatment were described using data from Kaiser Permanente of Southern California. Reports of such 'Reboud' hospitalizations or ED encounters occurred infrequently, representing <1% of Paxlovid-treated patients over the study period, reported the U.S. CDC on Jun. 24, 2022.

The U.S. CDC MMWR published on Jun. 21, 2022, stated 'The recurrence of COVID-19 symptoms after Paxlovid treatment might also be related to other factors, including viral reinfection or the emergence of treatment-resistant mutations.' The peer-review journal Clinical Infectious Diseases published a study on Jun. 14, 2022 that found (0.8%) of COVID-19 vaccinated Paxlovid users experienced 'Rebound' of symptoms, which were generally mild, at a median of 9 days after treatment, and all resolved without additional COVID-19-directed therapy.

On May 25, 2022, Pfizer representatives confirmed the company had not published information regarding secondary treatments after the initial five-day Paxlovid protocol. The U.S. CDC issued a Health Advisory CDCHAN-00467 on May 24, 2022: COVID-19 rebound has been reported to occur between 2 and 8 days after initial recovery and is characterized by a recurrence of COVID-19 symptoms or a new positive viral test after having tested negative. Limited information currently available from case reports suggests that persons treated with Paxlovid who experience COVID-19 rebound have had a mild illness. There are no reports of severe disease. There is currently no evidence that additional treatment is needed with Paxlovid or other anti-SARS-CoV-2 therapies in cases where COVID-19 rebound is suspected.

On May 24, 2022, the CDC's CDCHAN-00467 stated: 'A brief return of symptoms (COVID-19 Rebound) may be part of the natural history of SARS-CoV-2 coronavirus infection in some persons, independent of treatment with Paxlovid, and regardless of vaccination status.'

The U.S. FDA acknowledged cases on May 4, 2022, stating it 'was aware of the reports of some patients developing recurrent COVID-19 symptoms after completing a treatment course of Paxlovid.' And in the Paxlovid clinical trial, a small number of participants had one or more positive SARS-CoV-2 RT-PCR test results after testing negative or an increase in the amount of SARS-CoV-2 detected by PCR after completing their Paxlovid treatment course.

PAXLOVID Availability

As of Aug. 7, 2022, Paxlovid (Bexovid, nirmatrelvir, ritonavir) was authorized by about 65 countries, including Australia, Bahrain, Canada, ChinaEuropeIsrael, JapanGreeceSingapore, South AfricaSouth Korea, Switzerland, the United Kingdom, MalaysiaOntario, Quebec, New Brunswick, the Philippines, Taiwan, Malaysia, and Mexico. Pfizer forecasted the ability to produce up to 120 million courses of Paxlovid treatment by the end of 2022.

For the U.S. market, the U.S. Department of Health and Human Services Office of the Assistant Secretary for Preparedness and Response (ASPR) oversees the allocation of Paxlovid. On Jul. 6, 2022, the FDA authorized state-licensed pharmacists to prescribe Paxlovid. On Aug. 1, 2022, ASPR allocated 612,260 treatments for distribution in the USA. Per data from the Department of Health and Human Services, there were 1.26 million Paxlovid courses dispensed in July 2022, a 37% increase over June, reported Axios.

And beginning in Mar. 2022, generic versions of Paxlovid are being supplied in 95 low- and middle-income countries. In India, Zenara Pharma received Central Drugs Standard Control Organization approval to manufacture and market a generic version of Paxlovid under the brand name Paxzen.

PAXLOVID Drug Interactions

Pfizer confirms PAXLOVID is contraindicated in patients with a history of clinically significant hypersensitivity reactions to its active ingredients (nirmatrelvir or ritonavir) or any other components of the product and with drugs that are highly dependent on CYP3A for clearance and for which elevated concentrations are associated with serious and/or life-threatening reactions. Before prescribing ritonavir-boosted nirmatrelvir, clinicians should carefully review the patient's concomitant medications, including over-the-counter medicines, herbal supplements, and recreational drugs, says the U.S. NIH.

The FDA provided additional guidance on June 3, 2022, to help prescribers evaluate potential drug interactions when using Paxlovid therapy for COVID-19. Prescribers should review each patient's full list of medications and use other resources to evaluate for potential drug interactions in patients who take medications that are not included on the Fact Sheet or checklist at this time (a listing of additional resources is provided at the end of the checklist). Please see the updated Prescriber Patient Eligibility Screening Checklist for more information."

On May 6, 2022, the Infectious Diseases Society of America stated in Version 1.1, 'that given coformulation with ritonavir as a pharmacokinetic booster, there is potential for drug interactions.' And taking ritonavir with certain other medications may cause side effects.

On Feb. 24, 2022, the NIH published 'Ritonavir-boosted nirmatrelvir (Paxlovid) has significant and complex drug-drug interaction potential, primarily due to the ritonavir component of the combination. Boosting with ritonavir, a strong cytochrome P450 (CYP) 3A inhibitor, is required to increase the exposure of nirmatrelvir to a concentration that is effective against SARS-CoV-2. Ritonavir is an FDA-approved drug that has been used as a pharmacologic boosting agent for certain anti-HIV medications; therefore, there is a large body of literature describing its use with other drugs and its potential for serious and sometimes life-threatening drug-drug interactions.

On Feb. 16, 2022, the results from a phase 2/3 peer-reviewed study published by the NEJM found the incidence of adverse events that emerged during the treatment period was similar in the two groups (any adverse event, 22.6% with nirmatrelvir plus ritonavir vs. 23.9% with placebo; serious adverse events, 1.6% vs. 6.6%; and adverse events leading to discontinuation of the drugs or placebo, 2.1% vs. 4.2%). Dysgeusia (5.6% vs. 0.3%) and diarrhea (3.1% vs. 1.6%) occurred more frequently with nirmatrelvir plus ritonavir than with placebo.

Clinicians who are not experienced in prescribing ritonavir-boosted drugs should refer to resources such as the EUA fact sheet for ritonavir-boosted nirmatrelvir (Paxlovid) and the Liverpool COVID-19 Drug Interactions website for additional guidance. Furthermore, Viagra (sildenafil) must be used in low doses when used with protease inhibitors, especially Ritonavir.

PAXLOVID Ingredients

The two active substances of the medicine, PF-07321332, and ritonavir, are available as separate tablets. The EMA confirmed: (1R,2S,5S)-N-((1S)-1-Cyano-2-((3S)-2-oxopyrrolidin-3-yl)ethyl)-3-((2S)-3,3-dimethyl-2-(2,2,2-trifluoroacetamido) butanoyl)-6,6-dimethyl-3-azabicyclo[3.1.0]hexane-2-carboxamide; ritonavir.

PAXLOVID Dosage

In the U.S., Paxlovid is available by prescription only and should be initiated as soon as possible after a diagnosis of COVID-19 and within five days of symptom onset. PAXLOVID intends to be administered at a dose of 300 mg (two 150 mg tablets) of nirmatrelvir with one 100 mg tablet of ritonavir, given twice daily for five days. In addition, Paxlovid arrives in dose packs, and pharmacists remove one of the nirmatrelvir tablets from each dose of Paxlovid blisters before dispensing. One box contains five blister packs of PAXLOVID, as co-packaged nirmatrelvir tablets with ritonavir tablets, providing all required doses for an entire five-day treatment course.

On April 14, 2022, the U.S. FDA revised the EUA for Paxlovid. Paxlovid is now supplied in two different dose packs, one for standard dosing and one for moderate renal impairment dosing. In patients with moderate renal impairment (eGFR ≥30 to <60 mL/min), the dosage of Paxlovid is 150 mg nirmatrelvir (one 150 mg tablet) and 100 mg ritonavir (one 100 mg tablet) twice daily for five days. And for patients with mild renal impairment (eGFR ≥60 to <90 mL/min) should receive the standard dose of 300 mg nirmatrelvir (two 150 mg tablets) and 100 mg ritonavir (one 100 mg tablet) with all three tablets taken together orally twice daily for five days. Furthermore, Paxlovid is not recommended at this time in patients with severe renal impairment (eGFR <30 mL/min). 

The EMA says, 'Paxlovid must not be used with certain other medicines, either because its action may lead to harmful increases in their blood levels, or because conversely, some medicines may reduce the activity of Paxlovid itself. The list of medicines that must not be used with Paxlovid is included in the proposed conditions for use. Paxlovid must also not be used in patients with severely reduced kidney or liver function.'

On December 30, 2021, the U.S. NIH COVID-19 Treatment Guidelines Panel's Statement on Potential Drug-Drug Interactions Between Ritonavir-Boosted Nirmatrelvir (Paxlovid) and Concomitant Medications was updated. Please see Full EUA Prescribing Information at COVID19oralRx.com.

PAXLOVID Indication

PAXLOVID oral antiviral therapy prevents the SARS-CoV-2 virus from replicating in human host cells. PAXLOVID is the first 3CL protease inhibitor oral antiviral specifically designed to combat SARS-CoV-2. When administered as an early-stage treatment, Paxlovid might prevent COVID-19–related hospitalization among persons with mild-to-moderate COVID-19 who are at risk for progression to severe disease, stated the U.S. CDC's MMWR published on June 21, 2022.

The U.S. FDA authorized it to treat mild-to-moderate COVID-19 in adults and pediatric patients (12 years of age and older weighing at least 40 kilograms or about 88 pounds). Paxlovid is not authorized for the pre-exposure or post-exposure prevention of COVID-19 or initiation of treatment in those requiring hospitalization due to severe or critical COVID-19. 

The EMA's Committee for Medicinal Products for Human Use issued advice on the use of PAXLOVID (nirmatrelvir tablets and ritonavir tablets) on Jan. 27, 2022, stating that PAXLOVID can be used to treat adults with COVID-19 who do not require supplemental oxygen and who are at increased risk of progressing to severe disease. The EMA also recommends that PAXLOVID should be administered after a diagnosis of COVID-19 and within five days of the start of symptoms. 

However, data collected by FIND show that the average daily testing rate in low-income countries is as low as one-eightieth the rate in high-income countries. Only 21.5% of tests administered worldwide have been used in low- and lower-middle-income countries, despite these countries comprising 50.8% of the global population.

On Feb. 16, 2022, the NEJM published an Editorial that stated: 'it is worth considering the difference between absolute and relative risk reduction. Although the relative risk reductions were large and similar across most subgroups (at about 89%), those at lower risk had a very small absolute benefit. For example, in patients who were SARS-CoV-2 seronegative at baseline, the absolute risk reduction was about 10% points. However, in those who were SARS-CoV-2 seropositive at baseline, either because they had been infected in the past or had already undergone seroconversion from their current infection, the absolute risk reduction was about 1% point. Thus, although all groups seem to have a similar relative benefit, the greatest absolute benefit is among those at highest risk.'

The U.S. NIH says 'clinicians who are not experienced in prescribing ritonavir-boosted drugs should refer to resources such as the EUA fact sheet for ritonavir-boosted nirmatrelvir (Paxlovid). Before prescribing ritonavir-boosted nirmatrelvir (Paxlovid) for a patient receiving this immunosuppressant, the patient's provider should be consulted, given the significant drug-drug interaction potential between ritonavir and the narrow therapeutic index agent and because close monitoring may not be feasible.

PAXLOVID Women

The U.S. NIH stated on Feb 24, 2022, 'The EPIC-HR trial excluded pregnant and lactating individuals. Ritonavir has been used extensively during pregnancy in people with HIV, suggesting an acceptable safety profile during pregnancy. Based on the mechanisms of action for both nirmatrelvir and ritonavir and the available animal data, the Panel would not withhold ritonavir-boosted nirmatrelvir from a pregnant patient if the potential benefits outweighed the potential risks.'

The EUA for Paxlovid suggests that individuals who use products containing ethinyl estradiol for contraception should use a backup, nonhormonal contraceptive method because Paxlovid has the potential to decrease ethinyl estradiol levels. However, the enzyme-inducing effects of Paxlovid that would lead to lower hormone exposure are not expected to be clinically significant during five days of therapy and, therefore, would not be expected to decrease contraceptive effectiveness. In addition, ethinyl estradiol is always combined with a progestin for contraception. Progestin concentrations are expected to remain similar or increase when Paxlovid is used concomitantly with combined hormonal contraception, which maintains the effectiveness of the oral contraceptive.

PAXLOVID Children

In clinical trials, the safety and efficacy of using ritonavir-boosted nirmatrelvir with pediatric patients have not been established. Pfizer confirmed on Mar. 9, 2022; the EPIC-PEDS Phase 2/3 trial is an open-label, multi-center, single-arm study in approximately 140 pediatric participants under 18 years of age. Cohort 1 includes participants aged 6 to 17 weighing at least 88 lbs, and Cohort 2 includes those aged 6 to 17 weighing more than 44 lbs and less than 88 lbs. The WSJ reported on Mar. 9, 2022, that Pfizer expects results from a phase 2/3 clinical study of Paxlovid use in high-risk children by the end of 2022.

PAXLOVID and Cancer

MD Anderson in Houston, Texas wrote: Cancer and COVID-19: What protection do PAXLOVID, EVUSHELD therapies provide? On May 31, 2022, the U.S. NIH wrote: Special Considerations in Adults and Children With Cancer.

PAXLOVID Genetic

Under the terms of the head license agreement between Pfizer and MPP, announced on November 16, 2021, qualified generic medicine manufacturers worldwide that are granted sub-licenses will be able to supply PF-07321332 in combination with ritonavir to 95 countries, covering up to approximately 53% of the world's population. This agreement was expanded on March 17, 2022, to include 35 companies. Beximco Pharma markets Paxlovid under the brand name Bexovid, initially in Bangladesh. Manila confirmed on March 10, 2022, that it authorized Bexovid for those aged 12 and above.

Paxlovid Payments

In the U.S., Plaxovid is available by prescription only. CMS has released a set of toolkits for providers, states, and insurers to help the health care system prepare and swiftly administer COVID-19 products once they become available. On May 12, 2022, generic manufacturers stated Paxlovid was available to low- and middle-income countries at under $25 per treatment course. Pfizer Inc. sold PAXLOVID to the U.S. government for $529 per course in 2021. According to NPR's recent access to the U.S. agreement, the contract has a 'most favored nation pricing' clause and includes a buyback clause, meaning that if Paxlovid's emergency use authorization needs to be withdrawn.

Paxlovid Revenues

Pfizer Inc. reported on July 28, 2022, Paxlovid revenues of approximately $22 billion, which reflects favorable operational updates compared to prior guidance, offset by unfavorable incremental impacts from foreign exchange. This guidance includes treatment courses expected to be delivered in fiscal 2022, primarily relating to supply contracts signed or committed as of mid-July 2022.

Pfizer confirmed on February 8, 2022, that Paxlovid contributed $76 million in U.S. sales after the U.S. FDA authorized the COVID-19 treatment in late-December 2021. And Pfizer expects revenues of $22 billion from Paxlovid in 2022.

Paxlovid Legal Matters

Massachusetts-based Enanta Pharmaceuticals Inc. announced on June 21, 2022, that it filed a patent infringement suit against Pfizer Inc., seeking damages in the manufacture, use, and sale of Paxlovid.

Paxlovid News

July 30, 2022 - STATNews reported the U.S. president tested positive for COVID-19 after taking the antiviral Paxlovid. 

July 19, 2022 - Iowa based Hy-Vee, Inc. announced all Hy-Vee Pharmacy locations across its eight-state region now offer test-to-treat COVID-19 services using the COVID-19 antiviral, PAXLOVID.

July 14, 2022 - The Lancet Infectious Disease published a Correspondence - Paxlovid in patients who are immunocompromised and hospitalized with SARS-CoV-2 infection. Paxlovid prescription within 5 days of diagnosis had a faster clearance of viral load as measured by ORF1ab viral gene replication (appendix p 3) and a shorter time to viral elimination in patients who are immunocompromised (13·67 days [5·84] vs 19·17 days [5·87], p=0·022; appendix pp 6,7). In addition, the correlation between the timing of paxlovid initiation and viral elimination is linear

July 6, 2022 - The EMA published Paxlovid clinical data update: ((1R,2S,5S)-N-((1S)-1-Cyano-2-((3S)-2-oxopyrrolidin-3-yl)ethyl)-3-((2S)-3,3-dimethyl-2-(2,2,2-trifluoroacetamido) butanoyl)-6,6-dimethyl-3-azabicyclo[3.1.0]hexane-2-carboxamide / Ritonavir) EMEA/H/C/005973/0000.

June 30, 2022 - Pfizer Inc. announced a U.S. FDA submission that seeks approval for the treatment of COVID-19 vaccinated and unvaccinated individuals at high risk for progression to severe illness from COVID-19.

June 29, 2022 - Science.org published: Bad news for Paxlovid? Coronavirus can find multiple ways to evade COVID-19 drug.

June 28, 2022 - A non-peer-reviewed study - Naturally occurring mutations of SARS-CoV-2 main protease confer drug resistance to nirmatrelvir - The emergence of SARS-CoV-2 variants mutations in the Mpro raised the potential drug resistance. Overall, this study identified several drug-resistant hot spots that warrant close monitoring for possible clinical evidence of Paxlovid resistance.

June 14, 2022 - Pfizer Inc. announced pre-specified secondary endpoint resulted in a nominally significant 62% decrease in COVID-19-related medical visits per day across all patients, relative to placebo; In a sub-group analysis, a non-significant 57% reduction in hospitalizations and death was observed in PAXLOVID-treated vaccinated patients with at least one risk factor for severe COVID-19; Pfizer ceased enrollment into the EPIC-SR trial due to low rate of hospitalization or death in the standard-risk population; and will continue to evaluate treatment in populations with high unmet need. It also said Paxlovid did not have a significant impact on high-risk people who have been vaccinated.

June 6, 2022 - Pfizer Inc. announced it would further strengthen its commitment to U.S. manufacturing with a $120 million investment at its Kalamazoo, Michigan, facility, enabling U.S.-based production in support of its COVID-19 oral treatment, PAXLOVID.

June 2, 2022 - According to findings published in the peer review journal Clinical Infectious Diseases, both Paxlovid and adequate COVID-19 vaccination status were associated with a significant decrease in the rate of severe COVID-19 or mortality with adjusted HR 0.54 (95% CI, 0.39-0.75) and 0.20 (95% CI, 0.17-0.22), respectively. And Paxlovid appears to be more effective in older patients, immunosuppressed patients, and patients with underlying neurological or cardiovascular disease (interaction p-value <0.05 for all). No significant interaction was detected between Paxlovid treatment and COVID-19 vaccination status. Despite the shown effectiveness, it should be noted that Paxlovid is not recommended in several medical 6 conditions and has complex drug-drug interactions due to the ritonavir component of the combination.

June 1, 2022 - A non-peer-review Research Article based on data from Israel: Oral Nirmatrelvir and Severe Covid-19 Outcomes During the Omicron Surge, concluded - Nirmatrelvir therapy was associated with a 67% reduction in Covid-19 hospitalizations and an 81% reduction in Covid-19 mortality in patients 65 years and above. However, no significant benefit in avoidance of severe Covid-19 outcomes was shown in younger adults.

May 20, 2022 - A non-peer-reviewed study recently conducted in Hong Kong concluded 'Against Omicron BA.2, initiation of novel oral antiviral treatment in hospitalized patients not requiring any oxygen therapy was associated with lower risks of disease progression and all-cause mortality, in addition to achieving low viral load faster.' 

May 20, 2022 - The Swiss Confederation signed a contract with Pfizer SA for the purchase of 12,000 packs of Paxlovid. The first treatments will be possible as early as May 2022.

May 18, 2022 - Anthony Fauci, M.D., said "We're going to be planning what studies we're going to be doing relatively soon, within the next few days," during a White House COVID-19 briefing, regarding 'rebound' cases.

May 13, 2022 - Open Forum Infectious Diseases published: Supratherapeutic tacrolimus concentrations with nirmatrelvir/ritonavir in solid organ transplant recipients requiring hospitalization: A case series using rifampin for reversal - described two solid organ transplant recipients prescribed nirmatrelvir/ritonavir for outpatient use that developed tacrolimus toxicity requiring hospitalization and were managed with rifampin for toxicity reversal.

May 7, 2022 - Samiran Panda, head of epidemiology and infectious diseases at the Indian Council of Medical Research, told E.T. that members of the National Task Force on Covid-19 'did not find merit in Paxlovid inclusion in the treatment guidelines.

May 6, 2022 - Todos Medical, Ltd. reported a case of a patient with a history of multiple SARS-CoV-2 infections and persistent Acute Sequelae of SARS-CoV-2 (PASC), who received the therapeutic intervention Paxlovid following a positive PCR test and experienced a severe rebound of symptoms starting on Day 5, the final day of Paxlovid treatment. The patient's symptoms were resolved following an initial 14-day to cleanse with 3CL protease inhibitor immune support dietary supplement Tollovid®, a 3CL protease inhibitor and anti-cytokine therapeutic candidate for the treatment of the nidovirus subcategory of coronaviruses.

May 5, 2022 - STAT News reported only three incarcerated people have received Paxlovid. The U.S. federal government has allocated 160 doses of oral antiviral to federal prisons since December 2021.

April 29, 2022 - Pfizer Inc said a large trial found that Paxlovid was not effective at preventing coronavirus infection in people living with someone infected with the virus.

April 26, 2022 - Bloomberg News reported U.S. VP Harris began taking Paxlivod.

April 22, 2022 - The WHO strongly recommends that Pfizer make its pricing and deals more transparent and enlarge the geographical scope of its license with the Medicines Patent Pool so that more generic manufacturers may start to produce the medicine and make it available faster at affordable prices.

April 19, 2022 - Reuters reported demand for Paxlovid has been unexpectedly light.

April 12, 2022 - Yale Medicine wrote: 12 Things To Know About Paxlovid, the Latest COVID-19 Pill.

April 12, 2022 - CBC reported Alberta had 16,000 courses of Paxlovid in stock, and 670 prescriptions were filled since the drug became available at the end of January 2022.

April 11, 2022 - Taiwan's Central Epidemic Command Center announced that it had signed a purchase contract with Pfizer for 700,000 courses of Paxlovid.

April 11, 2022 - Malaysia is expected to receive 48,000 doses of Paxlovid. 

April 7, 2022 - The 55 Stop & Shop pharmacy locations in New York will now offer Paxlovid at no cost to customers.

April 7, 2022 -  CNA reported Taiwan has plans to procure additional Paxlovid from Pfizer, according to Minister of Health and Welfare Chen Shih-chung. Taiwan previously signed an agreement with Pfizer to procure 20,000 courses of Paxlovid, with the first batch containing 3,200 courses delivered on Jan. 27th.

March 30, 2022 - NPR reported: A new federal website aims to solve a key COVID problem: where to get antiviral pills.

March 24, 2022 - Local media in Florida confirmed Paxlovid is available at certain pharmacies.

March 22, 2022 - Pfizer Inc. announced today an agreement with UNICEF to supply up to 4 million treatment courses of PAXLOVID to 95 low- and middle-income countries, pending authorization or approval.

March 17, 2022 - The Medicines Patent Pool announced that it had signed agreements with 35 companies to manufacture the generic version of Paxlovid that can be supplied in 95 low- and middle-income countries.

March 17, 2022 - Quebec's government is expanding access to Paxlovid in pharmacies. COVID-19 patients must obtain a prescription from a physician or nurse practitioner following a positive test result.

March 12, 2022 - Bloomberg reported Merck may have challengers in meeting product demands in 2022.

March 9, 2022 - Pfizer Inc. announced it had initiated a Phase 2/3 study, EPIC-PEDS, with pediatric participants with a confirmed diagnosis of COVID-19 who are at risk of progression to severe disease.

March 8, 2022 - NPR reported - Test to Treat is an additional pipeline for COVID pills that intends to streamline the process. Currently, getting the pills can be time-consuming and complicated, says Dr. Cameron Webb, senior policy adviser for equity on the White House COVID-19 response team.

March 2, 2022 -  Reuters reported Pfizer is expected to provide about 10 million courses of Paxlovid to low- and middle-income countries in 2022, according to an official with the Global Fund.

February 14, 2022 - Local media reported China issued authorization for Paxlovid for certain people.

February 10, 2022 - Local media reported Paxlovid was granted fast-track approval for use in Japan by the health ministry.

February 8, 2022 - Pfizer, Inc. confirmed multiple studies demonstrating that the in vitro efficacy of nirmatrelvir, the active main protease inhibitor of Paxlovid, is maintained against the SARS-CoV-2 variant Omicron. Taken together, these in vitro studies suggest that Paxlovid has the potential to maintain plasma concentrations many-fold times higher than the amount required to prevent Omicron from replicating in cells.

February 4, 2022 - MIT Technology reported: How Pfizer made an effective anti-covid pill.

February 3, 2022 - The Health Sciences Authority granted interim authorization of Paxlovid, the first oral tablet approved in Singapore for COVID-19 treatment.

January 30, 2022 - Local media reported New York City Mayor Eric Adams confirmed the city will begin offering same-day, at-home delivery of COVID-19 oral antivirals, for free, but require a doctor's prescription. 

January 28, 2022 - The European Commission issued authorization to Pfizer Europe MA EEIG. 

January 27, 2022 - The EMA Committee recommended authorizing Paxlovid for treating COVID-19 in certain adults; the first COVID-19 oral antiviral recommended in the E.U.

January 25, 2022 - Media reported India's Subject Expert Committee is requiring local bioavailability and bioequivalence clinical studies and safety data prior to authorizing generic versions of Paxlovid for use in India.

January 22, 2022 - The WSJ reported: As Covid-19 Pills Roll Out, Worry Mounts That Resistance Could Develop.

January 21, 2022 - The journal Nature published a news article: The first crop of antivirals against SARS-CoV-2 is promising. But new drugs will be needed to counter the looming threat of resistance.

January 21, 2022 - Canadian media reported the first shipment of Paxlovid arrived in Ontario.

January 20, 2022 - The Australian Government welcomes the Therapeutic Goods Administration's provisional approval of the first oral Paxlovid® (nirmatrelvir + ritonavir).

January 18, 2022 -  Pfizer Inc. announced results from multiple clinical studies demonstrating the in vitro efficacy of nirmatrelvir, the active main protease inhibitor of PAXLOVID, is maintained against the SARS-CoV-2 virus variant known as Omicron.

January 17, 2022 - The Honourable Filomena Tassi, Minister of Public Services and Procurement, announced Canada has received an initial shipment of 30,400 treatment courses of PAXLOVID, with 120,000 more expected by the end of March 2022.

January 12, 2022 - According to the Kan public broadcaster, the first Paxlovid shipment consisted of 20,000 doses. Israel has signed a deal with Pfizer to purchase 100,000 doses overall, according to Hebrew media reports.

January 11, 2022 - The Philippines Food and Drug Administration granted a compassionate special permit for Bexovid, the first generic version of Pfizer's Paxlovid.

January 10, 2022 - The EMA announced 'Should the additional data submitted with the conditional marketing authorization application be sufficient to conclude that the benefits of Paxlovid outweigh its risks in the treatment of COVID 19, the EMA will liaise closely with the European Commission to fast track the decision granting a conditional marketing authorization in all E.U. and the EEA Member States.'

January 4, 2022 - Pfizer Inc. confirmed the U.S. government has now ordered a total of 20 million Paxlovid treatments for delivery in 2022.

December 31, 2021 - Dr. June Raine, MHRA Chief Executive, announced "Today we have given our regulatory approval for Paxlovid, a COVID-19 treatment found to cut COVID-19 related hospitalizations and deaths by 89% when taken within three days of the start of symptoms."

December 29, 2021 - Walmart Inc. announced Sam's Club and Walmart pharmacies are ready to receive and dispense Paxlovid as supplies allow.

December 26, 2021 - The Times of Israel announced the Health Ministry authorized Paxlovid.

December 22, 2021 - The U.S. FDA announced a EUA for Paxlovid (nirmatrelvir tablets and ritonavir tablets, co-packaged for oral use) for the treatment of mild-to-moderate COVID-19 in adults and certain pediatric patients with positive results of direct SARS-CoV-2 testing, and who are at high risk for progression to severe COVID-19, including hospitalization or death. Paxlovid is available by prescription only and should be initiated as soon as possible after a diagnosis of COVID-19 and within five days of symptom onset.

December 22, 2021 - Pfizer Inc. announced a new agreement with the United Kingdom government to supply an additional 2.5 million treatment courses of its investigational candidate PAXLOVID™, subject to local authorization. This brings the total amount of treatment courses to 2.75 million.

December 16, 2021 - The EMA advised that Paxlovid should be administered as soon as possible after a diagnosis of COVID-19 and within five days of the start of symptoms. The EMA issued this advice to support national authorities who may decide on the possible early use of the medicine before marketing authorization. If authorized, PAXLOVID could be prescribed as an at-home treatment to high-risk patients at the first sign of infection, potentially helping patients avoid severe illness, which can lead to hospitalization and death. PAXLOVID is also being studied in adults at risk of progressing to severe illness and adults exposed to the virus through household contacts.

December 14, 2021 - Science.org published an article: Pfizer's Paxlovid Holds Up - So Paxlovid looks to have the most effect when you'd want it the most, in patients who are at high risk of bad outcomes.

December 14, 2021 - Pfizer Inc. announced final results from its Phase 2/3 EPIC-HR trial analysis. These results were consistent with the interim analysis announced in November 2021, showing PAXLOVID significantly reduced the risk of hospitalization or death for any cause by 89% compared to placebo in nonhospitalized, high-risk adult patients with COVID-19 treated within three days of symptom onset. In addition, in a secondary endpoint, PAXLOVID reduced the risk of hospitalization or death for any cause by 88% compared to placebo in patients treated within five days of symptom onset, an increase from the 85% observed in the interim analysis.

December 3, 2021 - Filomena Tassi, Canada's minister of public services and procurement, told reporters the government had signed agreements with Pfizer Inc. to buy up to 1 million courses of PF-07321332.

November 29, 2021 - CNBC reported Pfizer estimates it can manufacture 80M treatment courses of Paxlovid, up from 50M projected a few weeks ago.

November 19, 2021 - The EMA announced it is reviewing currently available data on the use of Paxlovid to support national authorities who may decide on its use in emergency use settings before marketing authorization. 

November 18, 2021 - Pfizer Inc. announced an agreement with the U.S. government to supply 10 million treatment courses of PAXLOVID™ (PF-07321332; ritonavir), subject to regulatory authorization beginning later this year and concluding in 2022. Under the agreement terms, Pfizer will receive $5.29 billion from the U.S. government. Pricing for PAXLOVID is based on the principles of advance commitment, volume, equity, and affordability. The company has also entered into advance purchase agreements with several other countries and has initiated bilateral outreach to approximately 100 countries worldwide.

November 16, 2021 - Pfizer Inc. announced it is seeking Emergency Use Authorization of its investigational oral antiviral candidate, PAXLOVID™ (PF-07321332; ritonavir), for the treatment of mild to moderate COVID-19 in patients at increased risk of hospitalizations or death. Rolling submission of non-clinical data for PAXLOVID was initiated with the U.S. FDA in October 2021.

November 16, 2021 - Pfizer Inc. and the Medicines Patent Pool announced the signing of a voluntary license agreement for Pfizer's COVID-19 oral antiviral treatment candidate PF-07321332, which is administered in combination with low dose ritonavir (PF-07321332; ritonavir). The agreement will enable MPP to facilitate additional production and distribution of the investigational antiviral, pending regulatory authorization or approval, by granting sub-licenses to qualified generic medicine manufacturers to facilitate greater access to the global population.

November 13, 2021 - i24News reported an agreement with Pfizer has been reached. The Paxlovid shipment will be despatched as soon as Pfizer receives U.S. FDA approval.

November 10, 2021 - The journal Nature published an article: COVID antiviral pills: what scientists still want to know.

November 8, 2021 - The BMJ published an article: Commenting on the PAXLOVID announcement, England's health and social care secretary, Sajid Javid, said, "If approved, this could be another significant weapon in our armory to fight the virus alongside our vaccines and other treatments, including molnupiravir, which the U.K. was the first country in the world to approve this week."

November 5, 2021 - Pfizer Inc. announced its investigational novel COVID-19 oral antiviral candidate, PAXLOVID™, significantly reduced hospitalization and death, based on an interim analysis of the Phase 2/3 EPIC-HR randomized, double-blind study of nonhospitalized adult patients with COVID-19. They are at high risk of progressing to severe illness. The scheduled interim analysis showed an 89% reduction in risk of COVID-19-related hospitalization or death from any cause compared to placebo in patients treated within three days of symptom onset (primary endpoint); 0.8% of patients who received PAXLOVID™ were hospitalized through Day 28 following randomization (3/389 hospitalized with no deaths), compared to 7.0% of patients who received placebo and were hospitalized or died (27/385 hospitalized with seven subsequent deaths). The statistical significance of these results was high (p<0.0001). Similar reductions in COVID-19-related hospitalization or death were observed in patients treated within five days of symptom onset; 1.0% of patients who received PAXLOVID™ were hospitalized through Day 28 following randomization (6/607 hospitalized, with no deaths), compared to 6.7% of patients who received a placebo (41/612 hospitalized with ten subsequent deaths), with high statistical significance (p<0.0001). In addition, in the overall study population through Day 28, no casualties were reported in patients who received PAXLOVID™ as compared to 10 (1.6%) deaths in patients who received placebo.

October 5, 2021 - Australia announced the TGA had granted provisional determination to Pfizer Australia concerning a new combination medicine containing PF-07321332 and ritonavir to treat adult patients with symptomatic, confirmed coronavirus infection. The granting of an interim judgment means that the TGA has decided that Pfizer Australia is now eligible to apply for provisional registration of this treatment in the Australian Register of Therapeutic Goods.

September 27, 2021 - Pfizer Inc. announced the start of the Phase 2/3 EPIC-PEP study to evaluate the investigational novel oral antiviral candidate PF-07321332, co-administered with a low dose of ritonavir, for the prevention of COVID-19 infection. This Phase 2/3 trial is part of a global clinical research program. It enrolls individuals at least 18 years old and live in the same household as those with a confirmed symptomatic SARS-CoV-2 infection.

September 1, 2021 - Pfizer Inc. shared that the first participant has been dosed in a pivotal Phase 2/3 clinical trial to evaluate the safety and efficacy of PF-07321332 – an investigational orally administered protease inhibitor antiviral therapy explicitly designed to combat COVID-19 – in nonhospitalized, symptomatic adult participants who have a confirmed diagnosis of SARS-CoV-2 virus infection and are not at increased risk of progressing to severe illness, which may lead to hospitalization or death. 

July 28, 2021 - Pfizer today provided further details on its oral protease inhibitor program for the treatment of COVID-19. PF-07321332 exhibits potent, selective in vitro antiviral activity against SARS-CoV-2 and other coronaviruses. Additionally, it has demonstrated robust preclinical antiviral effects in human cells in vitro and SARS-CoV-2 infected animals. In Phase 1 pharmacokinetic study in healthy volunteers, PF-07321332 has shown high drug exposure over ten days, - 12 - exceeding the level of exposure predicted to inhibit SARS-CoV-2 viral replication by more than five-fold. Based on these data, Pfizer initiated a Phase 2/3 trial in COVID-19 patients in July 2021. Data from the trial are expected in the fourth quarter of 2021.

May 4, 2021 - Pfizer Inc. published today its 'Key Near-term Potential Milestones for COVID-19 Vaccine Program (2021)' on slide #8 within its financial report.

April 7, 2021 - Chemical & Engineering News published: Pfizer unveils its oral SARS-CoV-2 inhibitor.

March 23, 2021 - Pfizer Inc. announced that it is progressing to multiple ascending doses after completing the dosing of single ascending doses in a Phase 1 study in healthy adults to evaluate the safety and tolerability of an investigational, novel oral antiviral therapy for SARS-CoV-2, the virus that causes COVID-19. This Phase 1 trial is being conducted in the United States.

Paxlovid Clinical Trials

Clinical Trial: NCT04960202 - Treatment of symptomatic Covid-19 with nirmatrelvir plus ritonavir resulted in a risk of progression to severe Covid-19 that was 89% lower than the risk with placebo, without evident safety concerns. (Supported by Pfizer)

The Phase 2/3 EPIC-PEP trial is a randomized, double-blind, placebo-controlled study and will enroll up to 2,660 healthy adult participants aged 18 and older. Participants will be randomly assigned (1:1:1) to receive PF-07321332/ritonavir or placebo orally twice daily for 5 or 10 days. The primary objective will assess safety and efficacy to prevent confirmed SARS-CoV-2 infection and its symptoms through Day 14. PF-07321332 is an oral antiviral SARS-CoV-2-3CL protease inhibitor, which has an encouraging preclinical profile, including potent in vitro antiviral SARS-CoV-2 and broad coronavirus activity. Results from the Phase 1 clinical trial demonstrated that PF-07321332 was safe and well-tolerated.

A Phase 1, double-blind, sponsor open, single, and multiple ascending dose study evaluates the safety, tolerability, and pharmacokinetics of PF-07321332 in healthy participants.

For more information on the EPIC Phase 2/3 clinical trials for PAXLOVID, visit clinicaltrials.gov.