SAN DIEGO – A COVID-19 combination antiviral is the most important new drug primary care physicians have prescribed in recent years – plus it has helped keep many patients out of the hospital, according to a presenter at the annual meeting of the American College of Physicians.
Nirmatrelvir-ritonavir was granted emergency use authorization by the FDA late in 2021 to prevent progression to severe disease when COVID-19 cases and deaths were surging, and the Delta and Omicron variants started to spread.
Gerald Smetana, MD, an internist at Beth Israel Deaconess Medical Center in Boston, discussed nirmatrelvir-ritonavir as an example of how new drugs relevant to primary care can have a profound impact on public health.
Understanding the mechanism of action
Nirmatrelvir is the active agent of this combination and inhibits the SARS-CoV-2 main protease (Mpro), which is required for viral replication. In contrast to the SARS-CoV-2 spike protein, Mpro is highly conserved in coronaviruses and rarely acquires mutations. Therefore, unlike monoclonal antibodies targeting the spike protein, nirmatrelvir is active against known Omicron variants and is predicted to remain active against new variants that may emerge. The HIV1 protease inhibitor ritonavir has no activity against SARS-CoV-2. It can help increase the serum concentration of nirmatrelvir by inhibiting its metabolization.
“Although the details are not important for prescribing internists, having a basic understanding of the mechanism of action can help [doctors] better understand for which patients the drugs are indicated,” said Dr. Smetana, also a professor of medicine at Harvard Medical School, Boston. This is particularly important for newly approved drugs with a lot of new information to digest.
“Knowing the mechanisms of action of new drugs can help us predict their efficacy and potential side effects,” said Hubertus Kiefl, MD, an internist at Beth Israel Deaconess Medical Center and a lecturer at Harvard Medical School, during an interview after the session.
Understanding how drugs work also can help clinicians make better decisions, such as avoiding the use of a monoclonal antibody during a surge of a new variant with mutations in surface proteins or carefully managing the use of nirmatrelvir-ritonavir in patients who take certain medications that would cause potentially serious drug-drug interactions, Dr. Kiefl added.
Nirmatrelvir-ritonavir reduces the risk of hospitalization – but only in high-risk patients.
Dr. Smetana presented published data from the EPIC-HR study, a pivotal phase 2-3 clinical trial in 2,246 adult patients with COVID-19, all of whom were unvaccinated. Additionally, all patients had at least one risk factor for progression to severe disease.
When initiated 5 days after symptom onset or earlier, treatment with 300 mg nirmatrelvir plus 100 mg ritonavir twice a day for 5 days led to an 89% relative risk reduction in COVID-19–related hospitalization or death through day 28, compared with placebo.
Subgroup analyses showed that some patients benefited more than others. The highest risk reduction after treatment with nirmatrelvir-ritonavir was observed in patients at least 65 years old.
“It is important to remember that all the patients of this study were unvaccinated and [had] not had prior SARS-CoV-2 infection. This study population isn’t representative of most patients we are seeing today,” said Dr. Smetana.
Unpublished data from a study of standard-risk patients showed a nonsignificant reduction in the risk of hospitalization or death, he said. The study was stopped because of the low rates of hospitalization and death.
Effective in real world, but less so than in clinical trials
The fact that the patient cohort in the EPIC-HR trial was different from the patients internists see today makes real-world data critical for determining the usefulness of nirmatrelvir-ritonavir in everyday practice, Dr. Smetana said.
A real-world study from Israel conducted during the first Omicron wave (January to March 2022) showed that treatment with nirmatrelvir alone substantially reduced the relative risk of hospitalization in adults older than 65, with no evidence of benefit in adults aged 40-65. Dr. Smetana highlighted that, unlike the EPIC-HR cohort, most patients in the Israeli study had prior immunity due to vaccination or prior SARS-CoV-2 infection.
Many drug-drug interactions, but they can be managed
Nirmatrelvir-ritonavir interacts with many drugs, some of which are commonly used by primary care patients.
To help internists identify drug-drug interactions, Dr. Smetana proposed the use of the Liverpool COVID-19 Drug Interactions Checker, an intuitive tool that can help prescribers identify potential drug-drug interactions, categorize them based on severity, and identify management strategies.
This tool is specific to COVID-19 drugs. The Liverpool group also offers online drug interaction checkers for HIV, hepatitis, and cancer. “We need more tools like this to help improve the safe use of new drugs,” Dr. Smetana said.
To manage drug interactions, according to Dr. Smetana, U.S. treatment guidelines offer the following three options:
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Prescribe an alternative COVID therapy.
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Temporarily withhold concomitant medication if clinically appropriate.
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Adjust the dose of concomitant medication and monitor for adverse effects.
Medication doses that are withheld or modified should be continued through 3 days after completing nirmatrelvir-ritonavir, he added.
Important considerations
Commenting on things to consider for patients with COVID-19, Dr. Smetana said that there is a short window after symptom onset when nirmatrelvir-ritonavir can be prescribed, and safety in pregnancy is not known. There is also uncertainty regarding funding of nirmatrelvir-ritonavir prescriptions after the state of emergency is lifted. He reminded attendees that, although nirmatrelvir-ritonavir is the preferred first-line treatment for high-risk patients, another antiviral agent, molnupiravir, is also available and might be more appropriate for some patients.
He also cautioned about prescribing new drugs off label for indications that are not yet FDA-approved. “We are often stewards of limited resources when new drugs first become available but are not yet in sufficient supply to meet demand. Limiting our prescribing to FDA-approved indications helps to ensure equitable access,” he said.
Dr. Smetana and Dr. Kiefl reported no disclosures.
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