Background

Two new oral agents were given Emergency Use Authorization to be used in patients with mild-moderate COVID-19 at high risk of progression to severe infection, molnupiravir and nirmatrelvir/ritonavir (Paxlovid) [1,2]. Prior to this authorization, most evidence-based COVID therapies were parenteral and required significant healthcare resources to coordinate and administer.

Comparison

Nirmatrelvir/ritonavir [3]Molnupiravir [4]
Mechanism

Protease inhibitor leadings to interruption of viral replication

Ritonavir has no role in treating COVID-19, it is only included to boost levels of nirmatrelvir via CYP3A4 inhibition

Increased frequency of RNA mutations and impaired replication [5]
Efficacy vs Placebo (Hospitalization or Death)0.8% vs 6.3% (CI -7.21 to -4.03)6.8% vs 9.7% (CI -5.9 to -0.1)
Drug InteractionsCYP3A4 inducers, inhibitors, and substrates

May decrease efficacy of hormonal contraceptives, non-hormonal contraceptives should be considered

Contraindicated medications include: amiodarone, carbamazepine, clozapine, colchicine, dihydroergotamine, dronedarone, flecainide, lovastatin, ranolazine, sildenafil, simvastatin

Many other important interactions exist so care should be taken to assess all medication interactions

N/A
Cost*Patient: $0

US government: $530 [6]

Patient: $0

US Government: $700 [7]

Dose300 mg/100 mg BID for 5 days

Must be started within 5 days of symptom onset

800 mg BID for 5 days

Must be started within 5 days of symptom onset

NotesApproved for patients ≥ 12 years old AND ≥ 40 kg

Not approved for inpatient initiation

If patient is hospitalized, continuation is up to the discretion of the provider

Not used as pre-/post-exposure prophylaxis

Approved for patients ≥ 18 years

Not approved for inpatient initiation

If patient is hospitalized, continuation is up to the discretion of the provider

Not used as pre-/post-exposure prophylaxis

Renal/Hepatic Dose AdjustmentseGFR  ≥30 to <60 mL/min: 150 mg/100 mg BID

eGFR <30 mL/min: Not recommended

Child-Pugh class C: Not recommended

None

*Note: The US federal government has purchased 10 million doses of nirmatrelvir/ritonavir and 3 million doses of molnupiravir [8,9]. These supplies will be allocated to states and territories as needed and will be available to patients at no charge. 

Evidence:

Nirmatrelvir/ritonavir (Paxlovid)

Paxlovid was evaluated in the EPIC-HR trial, which is not fully published at this time [3]. This was a phase 2/3, double-blinded, randomized placebo controlled trial including nonhospitalized, unvaccinated patients adults with mild-moderate COVID-19 within 5 days of symptom onset with at least 1 risk factor for development of severe illness from COVID-19. Exclusion criteria included patients with a history of COVID-19 infection or COVID vaccination. Patients were given Paxlovid 300 mg/100 mg or placebo BID for 5 days. The primary outcome was hospitalization or death at day 28. The modified intention-to-treat1 (mITT1) group excluded patients who did not receive nor were expected to receive COVID-19 mAb treatment. In the mITT1 group, the primary outcome occurred in 0.8% of patients receiving Paxlovid vs 6.3% of patients in the placebo group (8/1039 vs 66/1046, CI -7.21 to -4.03).

These results appear quite robust with a fragility index of 37. Additionally, in patients with detectable COVID antibodies there was less of an impact of the study medication. However, these patients still appeared to have some benefit (0.2% vs 1.5%, CI -2.45 to -0.23) which suggests that vaccinated patients may still benefit from Paxlovid.

Risk factors for progression to severe disease: BMI >25, chronic lung disease, asthma, chronic kidney disease, current smoker, immunosuppressive disease or immunosuppressive treatment, cardiovascular disease, hypertension, sickle cell disease, neurodevelopmental disorders, active cancer, medically-related technological dependence, or age >60 years

Molnupiravir 

Molnupiravir was evaluated in the MOVe-OUT trial [10]. This was a phase 3, double-blinded, randomized, placebo controlled trial including nonhospitalized, unvaccinated adults with mild-moderate COVID-19 within 5 days of symptom onset with at least 1 risk factor for development of severe illness from COVID-19. Exclusion criteria included anticipated hospitalization within 48 hours, eGFR <30 or dialysis dependent, pregnancy, and COVID vaccination. Patients were able to receive steroids but not monoclonal antibodies (mAbs) nor remdesivir. Patients were given molnupiravir 800 mg or placebo BID for 5 days. The primary outcome was hospitalization or death at 29 days. In the mITT population, the primary outcome occurred in 6.8% of patients in the study group vs 9.7% in the placebo group (48/709 vs 68/699, CI -5.9 to -0.1). Death occurred in 1 patient on molnupiravir and in 9 patients on placebo (0.1% vs 1.3%, RRR 89%, CI 14 to 99).

Despite the above results, this may not be the positive trial it initially appears. First of all, for the primary outcome, the fragility index is 0, meaning that if 1 more patient in the study group experienced the primary outcome then it would have changed the statistical significance. Additionally, when the mITT analysis was adjusted for sex, the absolute risk reduction remained 2.8% but the confidence interval was not significant (-5.7 to 0.1). Lastly, in the subgroup analysis, there was no benefit in patients that had positive COVID antibody tests and there was a slight preference towards placebo over molnupiravir (3.7% vs 1.4%, ARR 2.3, CI -1.7 to 7.1). This suggests that vaccinated patients may not benefit from this therapy as much (or at all) as compared to unvaccinated patients.

Risk factors for progression to severe disease: age >60 years, active cancer, chronic kidney disease, COPD, BMI ≥30, heart failure, coronary artery disease, cardiomyopathy, or diabetes mellitus

Note: Both the EPIC-HR and MOVe-OUT studies were funded by their respective pharmaceutical company.

Bottom Line:

  • Nirmatrelvir/ritonavir (Paxlovid) and molnupiravir are approved under FDA EUAs for patients with mild-moderate COVID infection at high risk of severe disease within 5 days of symptom onset
  • Both medications appear to reduce death or hospitalization within a month, with most benefit likely to be experienced by unvaccinated patients
  • Nirmatrelvir/ritonavir (Paxlovid) appears to be more effective but also has many more drug interactions and contraindications

Want to learn more about EM Pharmacology?

Read other articles in the EM Pharm Pearls Series and find previous pearls on the PharmERToxguy site.

References:

  1. O’Shaughenessy J. Food and Drug Administration. Molnupiravir Emergency Use Authorization 108. December 23, 2021. https://www.fda.gov/media/155053/download
  2. O’Shaughenessy J. Food and Drug Administration. Nirmatrelvir/ritonavir Emergency Use Authorization 105. December 22, 2021. https://www.fda.gov/media/155049/download
  3. Nirmatrelvir/ritonavir. Package insert. Pfizer, Inc. 2021. https://www.fda.gov/media/155050/download
  4. Molnupiravir. Package insert. Merck Sharp & Dohme Corp. 2021. https://www.merck.com/eua/molnupiravir-hcp-fact-sheet.pdf
  5. Kabinger F, Stiller C, Schmitzová J, et al. Mechanism of molnupiravir-induced SARS-CoV-2 mutagenesis. Nat Struct Mol Biol. 2021;28(9):740-746. doi: 10.1038/s41594-021-00651-0. PMID: 34381216.
  6. Mishra M. U.S. to buy 10 mln courses of Pfizer’s COVID-19 pill for $5.3 bln. Reuters. Accessed January 12, 2022. https://www.reuters.com/business/healthcare-pharmaceuticals/us-govt-buy-10-mln-courses-pfizers-covid-19-pill-529-bln-2021-11-18/
  7. Willyard C. How antiviral pill molnupiravir shot ahead in the COVID drug hunt. Nature. Published online October 8, 2021. doi: 10.1038/d41586-021-02783-1. PMID: 34625735.
  8. Paxlovid (nirmatrelvir/PF-07321332 and ritonavir). U.S. Department of Health & Human Services: Office of the Assistant Secretary of Preparedness and Response. Updated: January 12, 2022. Accessed January 12, 2022. https://www.phe.gov/emergency/events/COVID19/investigation-MCM/Paxlovid/Pages/default.aspx
  9. Molnupiravir (MK-4482). U.S. Department of Health & Human Services: Office of the Assistant Secretary of Preparedness and Response. Updated: January 12, 2022. Accessed January 12, 2022. https://www.phe.gov/emergency/events/COVID19/investigation-MCM/molnupiravir/Pages/default.aspx
  10. Jayk Bernal A, Gomes da Silva MM, Musungaie DB, et al. Molnupiravir for oral treatment of covid-19 in nonhospitalized patients. N Engl J Med. Published online December 16, 2021. doi: 10.1056/NEJMoa2116044. PMID: 34914868.
Mike O'Brien, PharmD

Mike O'Brien, PharmD

ALiEM Series Editor, EM Pharm Pearls
EM Clinical Pharmacist
Massachusetts General Hospital
Mike O'Brien, PharmD

@MikeEMPharmD

Emergency Medicine Pharmacist at MGH | #FOAMed | Thoughts & views are my own