Drug Update · Infectious Disease

Nirmatrelvir/Ritonavir Cuts Hospitalization Risk 89% in EPIC-HR

July 18, 2026

Planned interim relative risk reduction

89.1% (EPIC-HR, patients treated ≤3 days after symptom onset) [1]

Final analysis relative risk reduction

88.9% (mITT population) [1]

Interim hospitalization incidence

0.77% (3/389) nirmatrelvir vs 7.01% (27/385) placebo [1]

Trial regimen

300 mg nirmatrelvir plus 100 mg ritonavir every 12 hours for 5 days (trial dose) [1]

Clinical Perspective

For clinicians treating nonhospitalized adults at high risk for progression to severe COVID-19, the EPIC-HR data support use of nirmatrelvir plus ritonavir to reduce the risk of Covid-19–related hospitalization or death, provided treatment can be initiated promptly after diagnosis and within 5 days of symptom onset ^[1]^[2]. The magnitude of benefit in the trial was large in the unvaccinated, high-risk population studied, and clinicians should weigh this benefit against the potential for clinically significant drug–drug interactions due to ritonavir ^[1]^[2]. Prescription requires review of concomitant medications for CYP3A interactions and attention to label contraindications and hepatic/renal dosing guidance ^[2].

Dr. Simran Kohli · Infectious Diseases

Nirmatrelvir plus ritonavir (PAXLOVID) reduced the risk of Covid-19–related hospitalization or death by approximately 89% in the EPIC-HR trial of symptomatic, nonhospitalized adults at high risk for progression to severe disease ^[1]. The phase 2–3 double-blind, randomized, placebo-controlled EPIC-HR study reported a relative risk reduction of 89.1% in a planned interim analysis and 88.9% in the final modified intention-to-treat analysis ^[1].

Clinical Context

Nirmatrelvir is an orally administered SARS-CoV-2 main protease (Mpro) inhibitor; ritonavir is co-administered as a pharmacokinetic enhancer and is an HIV-1 protease inhibitor and strong CYP3A inhibitor ^[2]^[3]. PAXLOVID is co-packaged by Pfizer and is indicated in adults at high risk for progression to severe COVID-19, including hospitalization or death, according to the U.S. prescribing information ^[2]. The EPIC-HR trial enrolled symptomatic, unvaccinated, nonhospitalized adults considered at high risk for progression, and the program evaluated clinical progression, viral load, and safety ^[1]. The product label emphasizes initiation as soon as possible and within 5 days of symptom onset and warns about significant drug-drug interactions due to ritonavir-mediated CYP3A inhibition ^[2].

Key Findings

In the planned interim analysis of EPIC-HR among patients treated within 3 days after symptom onset (modified intention-to-treat population), nirmatrelvir plus ritonavir lowered the incidence of Covid-19–related hospitalization or death through day 28 by 6.32 percentage points (relative risk reduction, 89.1%); incidence was 0.77% (3 of 389 patients) in the nirmatrelvir group versus 7.01% (27 of 385 patients) in the placebo group, with 0 deaths in the nirmatrelvir group and 7 deaths in the placebo group ^[1].
In the final analysis of the modified intention-to-treat population, efficacy was maintained with a difference of -5.81 percentage points (95% CI, -7.78 to -3.84; P<0.001; relative risk reduction, 88.9%); all 13 deaths reported in the trial occurred in the placebo group ^[1].
Antiviral activity was demonstrated by a lower viral load at day 5 when treatment was begun within 3 days of symptom onset, with an adjusted mean difference of -0.868 log10 copies per milliliter versus placebo ^[1].

Safety & Tolerability

The incidence of adverse events during the treatment period was similar between groups in EPIC-HR: any adverse event occurred in 22.6% with nirmatrelvir plus ritonavir versus 23.9% with placebo; serious adverse events occurred in 1.6% versus 6.6%; and adverse events leading to discontinuation occurred in 2.1% versus 4.2% ^[1]. Dysgeusia occurred more frequently with nirmatrelvir plus ritonavir (5.6% vs. 0.3%) and diarrhea was more frequent (3.1% vs. 1.6%) ^[1]. The product label carries a boxed warning about significant drug interactions because ritonavir is a strong CYP3A inhibitor and may increase exposure of concomitant medications, potentially resulting in severe or life-threatening events ^[2]. The label also notes reported hypersensitivity reactions, potential hepatotoxicity associated with ritonavir, and a risk of HIV-1 resistance development in individuals with uncontrolled or undiagnosed HIV-1 infection ^[2].

Study Design

EPIC-HR was a phase 2–3, double-blind, randomized, placebo-controlled trial that enrolled symptomatic, unvaccinated, nonhospitalized adults judged to be at high risk for progression to severe COVID-19; patients were randomized 1:1 to receive nirmatrelvir plus ritonavir or placebo ^[1]. A total of 2,246 patients underwent randomization (1,120 to nirmatrelvir plus ritonavir and 1,126 to placebo) in the overall trial population, and the primary endpoint was Covid-19–related hospitalization or death from any cause through day 28 ^[1]. The trial evaluated efficacy in modified intention-to-treat populations defined by timing of symptom onset and included virologic and safety assessments ^[1]. The trial regimen tested was 300 mg nirmatrelvir plus 100 mg ritonavir every 12 hours for 5 days ^[1]. Clinicians should consult current prescribing information for full dosing guidance.

FAQ

Q1 What is nirmatrelvir plus ritonavir (PAXLOVID) approved for?

PAXLOVID is indicated for the treatment of mild-to-moderate coronavirus disease 2019 (COVID-19) in adults who are at high risk for progression to severe COVID-19, including hospitalization or death, and is co-packaged as nirmatrelvir tablets with ritonavir tablets. The prescribing information states the treatment course should be initiated as soon as possible after diagnosis and within 5 days of symptom onset.

Q2 How does nirmatrelvir plus ritonavir work?

Nirmatrelvir is an oral SARS-CoV-2 main protease (Mpro) inhibitor that targets viral replication. Ritonavir is included as a pharmacokinetic enhancer; ritonavir inhibits CYP3A-mediated metabolism of nirmatrelvir to increase nirmatrelvir plasma concentrations. Ritonavir itself is an HIV-1 protease inhibitor and is not active against SARS-CoV-2 Mpro.

Q3 What is the recommended dose of PAXLOVID?

The recommended dosage for PAXLOVID in adults without renal impairment is 300 mg nirmatrelvir (two 150 mg tablets) with 100 mg ritonavir (one 100 mg tablet), all taken together orally twice daily for 5 days. Treatment should be started as soon as possible after diagnosis and within 5 days of symptom onset. Clinicians should consult current prescribing information for complete dosing guidance.

Q4 What are the most common side effects and key safety considerations?

In the EPIC-HR trial, dysgeusia and diarrhea were reported more frequently with nirmatrelvir plus ritonavir than with placebo (dysgeusia 5.6% vs 0.3%; diarrhea 3.1% vs 1.6%), and overall adverse event rates were similar between groups. The product labeling includes a boxed warning regarding potentially significant drug–drug interactions because ritonavir is a strong CYP3A inhibitor; the label also notes reported hypersensitivity reactions and potential hepatotoxicity and highlights the risk of HIV-1 resistance development in individuals with uncontrolled or undiagnosed HIV-1 infection. Clinicians should review concomitant medications for interactions before prescribing.

Clinicians should consult current prescribing information for complete dosing guidance.

Nirmatrelvir/Ritonavir Cuts Hospitalization Risk 89% in EPIC-HR

Nirmatrelvir/Ritonavir Cuts Hospitalization Risk 89% in EPIC-HR

Clinical Perspective

Clinical Context

Key Findings

Safety & Tolerability

Study Design

FAQ

References

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