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Study of ibuzatrelvir tablets in non-hospitalized adults and adolescents with COVID-19 who are at high risk of developing severe illness

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What is this trial about?

A plain-language summary of the goals, design and what participants do

This study focuses on treating people with COVID-19 who are not in the hospital but have a high risk of developing severe illness. The study will test a new medication called ibuzatrelvir, which comes as a film-coated tablet that is taken by mouth. Some participants will receive ibuzatrelvir while others will receive a placebo.

The purpose of this research is to determine how well ibuzatrelvir works compared to placebo in treating people with COVID-19 who are at high risk of their condition becoming worse. The study will include both adults and adolescents who weigh at least 40 kilograms (about 88 pounds) and who cannot or choose not to take other available COVID-19 treatments.

During the study, participants will take either ibuzatrelvir tablets or placebo tablets. The researchers will monitor participants for 28 days to see if they need emergency care, require oxygen support, need additional treatments, are hospitalized, or experience other health issues. They will also track how quickly symptoms improve and check for any lasting effects of COVID-19 for up to 24 weeks after treatment begins.

The research process

The trial runs in 5 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial screening

    Your eligibility will be verified based on age (12 years and older, with weight at least 40 kg for ages 12-17) and presence of risk factors for severe COVID-19

    A nasal test called RAT (Rapid Antigen Test) will confirm your COVID-19 infection within 24 hours before starting the study

    It will be confirmed that you are unable or unwilling to take nirmatrelvir/ritonavir treatment

  2. Step 2

    Treatment assignment

    You will be randomly assigned to receive either ibuzatrelvir tablets or placebo tablets (tablets without active medication)

    Neither you nor your doctor will know which treatment you are receiving

  3. Step 3

    Treatment period

    You will take the assigned tablets by mouth

    Your symptoms will be monitored for 28 days

    Any emergency department visits, need for oxygen, additional treatments, hospitalizations, or other medical events will be recorded

  4. Step 4

    Follow-up period

    You will be monitored for up to 24 weeks after starting treatment

    The medical team will assess for any long-term COVID symptoms

    Your health status will be evaluated throughout this period

  5. Step 5

    Study completion

    Final health assessment will be performed at week 24

    Your participation in the study will end after completing all required evaluations

Who can join the trial?

5 criteria

  • Must be at least 12 years old and weigh at least 40 kg, or be 18 years or older of any weight
  • Must have risk factors that could make COVID-19 more severe, based on age (for example, older adults are at higher risk)
  • Must have a positive COVID-19 test from a rapid antigen test (RAT) using a nasal swab taken within 24 hours before starting the study
  • Must be unable or unwilling to take nirmatrelvir/ritonavir (which is another COVID-19 treatment medication)
  • Both men and women can participate in the study

Who cannot join the trial?

12 criteria

  • Patients who are hospitalized due to COVID-19
  • Patients who require supplemental oxygen therapy (extra oxygen support)
  • Individuals who have previously received COVID-19 antiviral treatments for their current infection
  • Patients with severe liver problems or abnormal liver function tests
  • People with known allergies to ibuzatrelvir or its components
  • Pregnant or breastfeeding women
  • Patients taking medications that may interact with ibuzatrelvir
  • People who have participated in another clinical trial within the past 30 days
  • Patients with uncontrolled chronic conditions (such as diabetes or high blood pressure that is not well-managed)
  • Individuals who have received monoclonal antibody therapy (specialized protein treatments) for COVID-19
  • People who cannot take oral medications
  • Patients with severe kidney disease requiring dialysis
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Investigated drugs

Ibuzatrelvir is an oral antiviral medication being studied for treating COVID-19. It is designed to help people who have COVID-19 but are not hospitalized and are at high risk of their illness becoming more severe. The medication works by targeting the virus that causes COVID-19, aiming to reduce the severity of the infection and prevent the disease from progressing to a more serious state.

What is already known about the treatment

Ibuzatrelvir – An oral antiviral medication being investigated in clinical trials for treating COVID-19 in non-hospitalized patients who are at high risk of developing severe illness. This novel drug belongs to the class of antiviral agents that specifically target SARS-CoV-2, the virus responsible for COVID-19. It is administered in tablet form and is currently being evaluated in Phase 3 clinical trials to determine its efficacy and safety compared to placebo, focusing on preventing disease progression in high-risk individuals who are not hospitalized.

Investigated diseases

  • COVID-19

    A respiratory disease caused by the SARS-CoV-2 virus that primarily affects the lungs and respiratory system. The infection typically begins with symptoms such as fever, cough, fatigue, and loss of taste or smell. In some cases, the disease can progress from mild to more severe symptoms, particularly in individuals with certain risk factors. The condition can affect multiple body systems and may lead to varying degrees of respiratory difficulties. Some people may develop longer-lasting symptoms known as Long COVID, where effects persist beyond the initial infection period.

  • Long COVID

    A condition where symptoms persist or develop after the initial COVID-19 infection has resolved. Symptoms can include ongoing fatigue, shortness of breath, cognitive difficulties (often called "brain fog"), muscle weakness, and various other physical and neurological effects. The condition can affect daily activities and may fluctuate in intensity over time. Long COVID can occur even in people who had mild initial COVID-19 symptoms.

Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2024-517727-39-00Protocol codeC5091017Estimated enrolment2 330 patientsSponsorPfizer Inc.

sourced from the EU Clinical Trials Register and site verification

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