SAN DIEGO – – 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.