Pfizer's "Overwhelming" COVID-19 Pill Results Fuel Home Treatment Hopes

Pfizer has announced the results of its Phase 2/3 Evaluation of Protease Inhibition for COVID-19 in High-Risk Patients (EPIC-HR) interim analysis, revealing that its antiviral pill Paxlovid reduced the risk of hospitalization and death by 89-percent in high-risk adults who had COVID-19. The protective effect was compared to a group of patients who received a placebo drug, paving the way for a potential new at-home treatment that may drastically reduce the number of hospitalizations.

Pfizer's Paxlovid is a novel oral antiviral pill developed as a potential treatment against severe COVID-19. The drug is a protease inhibitor that specifically blocks SARS-CoV-2 protease activity — that is, it blocks the enzyme the virus uses to replicate, an activity that potentially leads to more severe infections and increases the risk of death.

Paxlovid is the candidate oral treatment PF-07321332 administered alongside a low dose of ritonavir, an antiretroviral drug. By combining the SARS-CoV-2 protease inhibitor with the antiretroviral drug, Pfizer says its antiviral therapy enables PF-07321332 to stay active in the patient's body for a longer period of time while maintaining a higher concentration, making it more effective against the virus.

Pfizer announced the interim analysis results of its Phase 2/3 EPIC-HR study on November 5, stating that Paxlovid significantly reduced the risk of hospitalization and death from COVID-19 among high-risk patients. When looking at the overall participants in the study, none of the patients who received Paxlovid died over the course of 28 days compared with 10 patients who received the placebo and died from the disease.

The participants enrolled in the Phase 2/3 EPIC-HR study in late September; data on a total of 1,219 adult patients were used in the primary analysis the company has published. All of the participants had COVID-19 infections confirmed using lab tests, with the confirmation made within a five-day period and the symptoms ranging from mild to moderate.

Likewise, all of the participants had at least one factor that increased their risk of developing a severe infection. Over the course of five days, the participants were randomly split into two groups, one given the placebo and the other given Paxlovid every 12 hours.

The analysis found that Pfizer's oral antiviral COVID-19 therapy cut the risk of severe outcomes by 89-percent, with few participants reporting "adverse events," the majority of which were mild. Compared to the placebo drug, fewer patients who received Paxlovid experienced "serious adverse events" at 1.7-percent compared to 6.6-percent.

The interim analysis results are just one step toward potential authorization and eventual approval of Paxlovid, which isn't yet available to patients. The results are promising and as such, Pfizer says that it is following a recommendation from an independent data monitoring committee to stop enrolling additional patients in the study.

The reason for this decision is "the overwhelming efficacy demonstrated in these results," Pfizer explains, noting that it has plans to submit this data to the FDA as part of a rolling submission for an eventual Emergency Use Authorization (EUA). The drug has not been authorized or approved at this time.

Assuming Pfizer does eventually get an emergency use authorization from the FDA for Paxlovid, the drug would be the first oral antiviral treatment of its kind designed to address SARS-CoV-2, reduce the risk of severe COVID-19 infections, and potentially decrease the number of hospitalizations caused by the disease. In addition to reducing the severity of the illness in patients, Pfizer says its drug may also have potential for reducing the odds someone will develop an infection if they've been exposed to SARS-CoV-2.