Paxlovid is the brand name of a new oral antiviral medication PF-07321332 along with another antiviral medication, ritonavir.
Paxlovid has shown to reduce the risk of hospitalization or death by 89% versus placebo in non-hospitalized high-risk adults with COVID-19.
In theory, both new antiviral oral medications Lagevrio and Paxlovid should work against different COVID-19 variants. COVID-19 variants are primarily characterized by changes in the viral spike protein. These spike proteins are the targets of vaccines and monoclonal antibody therapies which is why some monoclonal antibody therapies have shown to be ineffective against certain COVID-19 variants.
Paxlovid and Lagevrio’s mechanisms of action are independent of different COVID-19 variant’s spike proteins and therefore should work for all variants. While this still needs to be shown in studies, it is a promising sign of their efficacy for current and new emerging variants.
According to the FDA’s Emergency Use Authorization, only physicians, physician assistants, and RNs can prescribe Paxlovid. Patients will need to be assessed by one of those professionals in order to receive care.
Individual states may change this policy. We will update this page if any state enables pharmacists to prescribe Paxlovid directly to patients. We also have an open letter you can co-sign to advocate for pharmacists’ ability to prescribe Paxlovid.
Paxlovid will likely be free to the general US population as the Biden administration has bought 10 million courses of the medication from Pfizer. The medication will be included in the US government’s emergency response.
As for non-governmental use of the medication, paxlovid will most likely be covered under most private health insurances.
Paxlovid is being studied in patients who are symptomatic and newly infected with COVID-19. If approved, Paxlovid will be used for the treatment of patients with mild-to-moderate COVID-19 who test positive for the virus and have risk factors for progressing to cases of severe illness caused by COVID-19 resulting in possible hospitalization or death. Conditions that have been found to most commonly predict progression to severe cases of COVID-19 include patients who may be 60 years of age or older, obese, have diabetes mellitus, or have hearth disease.
Paxlovid is a combination medication of PF-07321332 and ritonavir. PF-07321332 works by inhibiting an enzyme needed to process some COVID-19 proteins to their final form. Ritonavir, on the other hand, works by inhibiting our own liver enzymes from breaking down PF-07321332. This is worth noting because ritonavir affects how other medications are metabolized by our body. A physician should consider the patient’s current medication list before prescribing Paxlovid.
The study investigating paxlovid’s efficacy in treating COVID-19 is called the Phase 2/3 EPIC-HR (Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients). The Phase 2/3 EPIC-HR study is an ongoing randomized, double-blind study of non-hospitalized adult patients with COVID-19, who are at high risk of progressing to severe illness. While the study is still not finalized, interim analysis demonstrates paxlovid reducing the risk of hospitalization or death by 89% compared to placebo in non-hospitalized high-risk adults with COVID-19. By day 28, 10 deaths were reported in patients who received placebo compared to no deaths in the paxlovid group.
The primary analysis of the interim data set included data from 1219 adults enrolled in the study by September 29,2021. The study included patients in clinical trial sites across North and South America, Europe, Africa, and Asia, with 45% of patients located in the United States. Patients enrolled all had a laboratory confirmed positive diagnosis of COVID-19 within 5 days of enrollment and demonstrating mild-to-moderate symptoms along with at least one characteristic making them high-risk of developing severe illness from COVID-19. Each patient in the study was randomly assigned in a 1 to 1 ratio to either receive paxlovid or placebo twice daily for 5 days.
COVID-19 genomes encode two overlapping large polyproteins that are cleaved by 3C-like cysteine protease (3CLpro) which is critical for viral replication.This is a post-translational processing step and is seen in both COV-1 and COV-2 viruses in a identical fashion. The PF-07321332 component of paxlovid works by inhibiting 3CLpro via covalent inhibition by binding directly to the cysteine (Cys145) residue of the protease rendering it inactive.
Ritonavir is an antiviral medication that has historically been used as a treatment for HIV. Ritonavir works against HIV via competitive inhibition of HIV protease, an enzyme involved in the replication of HIV. In paxlovid, ritonavir works by inhibiting cytochrome P450 3A4, the major human hepatic drug-metabolizing enzyme. Without ritonavir, the PF-07321332 component of paxlovid would be broken down by our body’s liver enzymes before being allowed to act against COVID-19.
Paxlovid is administered by mouth at a dose of two 150 mg tablets (300 mg total) of PF-07321332 and one 100 mg tablet of ritonavir, given twice daily for 5 days.
Adverse events related to treatment with paxlovid and placebo were comparable at 19% and 21% respectively. Pfizer states that nausea and vomiting occurs in about 20% of patients taking the medication.
Contraindcations/cautions:
Active HIV infection, active Hepatitis B or C infection, liver disease, kidney disease
Major drug-drug interactions with ritonavir: cobicistat, cabotegravir
Contraindications to ritonavir: Alfuzosin, amiodarone, dronedarone, flecainide, propafenone, quinidine, voriconazole, colchicine, lurasidone, pimozide, dihydroergotamine, ergotamine, methylergonovine, cisapride, st. John’s Wort, lovastatin, simvastatin, sildenafil (when used for pulmonary arterial hypertension), oral midazolam, triazolam
Pregnancy/Lactation: No data available
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