A Phase 3 interventional study of ibuzatrelvir and remdesivir in COVID-19 Infection, sponsored by Pfizer. Recruiting at 159 sites in 18 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-10-14.
Sponsored by Pfizer · Phase 3, Interventional, and Treatment
This is a Phase 3, randomized, actively controlled, double-blinded, double-dummy, superiority study to evaluate the efficacy and safety of ibuzatrelvir alone and in combination with remdesivir IV compared to remdesivir IV alone for the treatment of symptomatic COVID-19 in severely immunocompromised adult participants who are non-hospitalized or are hospitalized at baseline with mild-to-moderate COVID-19.
The purpose of this clinical trial is to learn about a study medicine called Ibuzatrelvir for the possible treatment of COVID-19 in immunocompromised patients. Immunocompromised patients with COVID-19 have more difficulty fighting infections and are at risk for persistent infections and progression to severe illness. This patient population may benefit from extended antiviral treatment durations, or a combination of antiviral therapies. This study will evaluate the efficacy and safety of ibuzatrelvir with and without remdesivir compared with remdesivir alone for the treatment of symptomatic COVID-19 in adult participants who are severely immunocompromised.
The study is seeking adult male and female participants who:
All of the participants in this study will receive active treatment for COVID-19, and will be randomized to one of three treatment arms. One-third will received remdesivir, one-third will receive ibuzatrelvir, and one third will receive both remdesivir and ibuzatrelvir. Ibuzatrelvir will be taken by mouth twice daily, and remdesivir is given as an IV infusion daily. Placebos that look like the study medicines but do not have any medication will be given to make the 3 treatment arms appear to be the same. The study will compare the experiences of people receiving ibuzatrelvir with and without remdesivir to those of the people who only received remdesivir for COVID-19. This will help decide if ibuzatrelvir is safe and effective.
Participants will attend about 10 study visits over 24 weeks. During this time, they will have:
7,990 studies on the registry are indexed under COVID-19; 466 are open to participants now.
This study's planned enrollment of 300 is above the median of 102 across 4,364 interventional studies indexed under COVID-19.
Browse COVID-19 studies →Pfizer is the lead sponsor of 3,334 studies on the registry; 149 are open to participants now.
Of its 601 completed or terminated interventional studies of FDA-regulated products, 391 (65%) have results posted.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Severely due to:
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
GFR (glomerular filtration rate) is how much blood the kidneys filter each minute. It is usually estimated from a blood test — eGFR, by formulas such as CKD-EPI or MDRD — and some studies ask for it to be measured directly instead. Usually given in mL/min/1.73 m².
Check the method, the units and the minimum the study states. A value of 90 or above is in the normal-or-high range, but kidney damage can show in other tests too.
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
The study doctor’s estimate of how long someone is likely to live. Criteria use it so that people can stay in the study long enough for it to answer its question.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Immunosuppression
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Cancer (malignancy)
Malignancy means cancer. Criteria about another or earlier malignancy ask whether you have had a different cancer, usually within a set number of years.
Some are commonly allowed, such as treated skin cancers other than melanoma and early cancers removed completely — check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
GFR and eGFR (kidney filtering)
GFR (glomerular filtration rate) is how much blood the kidneys filter each minute. It is usually estimated from a blood test — eGFR, by formulas such as CKD-EPI or MDRD — and some studies ask for it to be measured directly instead. Usually given in mL/min/1.73 m².
Check the method, the units and the minimum the study states. A value of 90 or above is in the normal-or-high range, but kidney damage can show in other tests too.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hypersensitivity
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraindication
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Life expectancy
The study doctor’s estimate of how long someone is likely to live. Criteria use it so that people can stay in the study long enough for it to answer its question.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants will receive ibuzatrelvir orally twice a day + IV remdesivir
Drug: ibuzatrelvir · Drug: remdesivir
Participants will receive ibuzatrelvir orally twice a day + IV placebo for remdesivir
Drug: ibuzatrelvir · Drug: placebo for remdesivir
Participants will receive placebo for ibuzatrelvir orally twice a day + IV remdesivir
Drug: remdesivir · Drug: placebo for ibuzatrelvir
tablet
injection, for intravenous use
Also known as: veklury
tablet
injection, for intravenous use
The difference in the proportion of patients meeting the primary composite endpoint, between ibuzatrelvir and remdesivir vs remdesivir groups in symptomatic adult participants with COVID-19 who are severely immunocompromised
The difference in the proportion of participants with the composite endpoint of a) Progression to severe COVID-19 or all-cause mortality by Day 38, or b) Evidence of recurrent or persistent SARS-CoV-2 infection
Time frame: 38 days
Time to sustained alleviation of all targeted COVID-19 symptoms
The difference in median time to sustained alleviation of all targeted symptoms. Symptoms will be assessed through a daily electronic diary and include sore throat, cough, fever and diarrhea, among others.
Time frame: 38 days
Proportion of participants with evidence of recurrent or persistent SARS-CoV-2 infection.
The viral load is measured in nasal or nasopharyngeal samples using reverse transcription polymerase chain reaction (RT-PCR)
Time frame: 38 days
Proportion of participants with COVID-19-related ED visits with medical intervention, COVID-19-related hospitalization, or all-cause mortality.
Proportion of participants with COVID-19-related ED visits with medical intervention, COVID-19-related hospitalization, or all-cause mortality.
Time frame: 38 days
Change from baseline in SARS-CoV-2 RNA level in NP or nasal swabs over time
The viral load is measured in nasal or nasopharyngeal samples using reverse transcription polymerase chain reaction (RT-PCR)
Time frame: 38 days
Proportion of participants with SARS-CoV-2 NP or nasal RNA <LLOQ at each time point
Proportion of participants with a SARS-CoV-2 viral load below the lower limit of quantification (LLOQ) of the assay used to measure it.
Time frame: 38 days
Proportion of participants with viral rebound in SARS-CoV-2 RNA level in NP or nasal swabs
Virologic rebound is defined as: * Viral RNA is not detectable at the end of treatment, and later is detectable through Day 38 * Viral RNA is detected at end of treatment, and viral RNA levels increase further through Day 38
Time frame: 38 days
Time to sustained NP or nasal swab SARS-CoV-2 RNA <LLOQ
The time it takes for the viral RNA to no longer be detectable in a sample
Time frame: 38 days
Incidence of Treatment emergent adverse events, serious adverse events, and adverse events leading to discontinuation
An adverse event (AE) is any untoward medical occurrence in a participant, temporarily associated with the use of study intervention, whether or not considered related to the study intervention. Serious adverse event (SAE) is any untoward medical occurrence that, at any dose: resulted in death; required inpatient hospitalization or prolongation of existing hospitalization; was life-threatening; resulted in persistent or significant disability/ incapacity; congenital anomaly/birth defect; a suspected transmission via a Pfizer product of an infectious agent, pathogenic or non-pathogenic and other important medical events. AEs included both SAEs and all non-SAEs. An AE is considered as TEAE if the event started on or after start date of study intervention.
Time frame: 38 days
Showing the first 100 of 159 sites across 18 countries. Choose a country and city above to see the rest.
Plan to share: Yes — Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical_trials/trial_data_and_results/data_requests.
Data sharing details ↗ · www.pfizer.com
Started Jul 2025 (actual). Primary completion is estimated for Sep 2027, 26 months after the start.
Of 168 industry-sponsored phase 3 interventional studies under COVID-19, half reached primary completion within 8 months of starting (the median), counting those still running; a quarter within 4 and three quarters within 16. This study's planned 26 months is above that.
Counting every sponsor, half of 453 studies reached it within 9 months; a quarter within 4 and three quarters within 17.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
Eligibility is decided by the study team. Share this record with your doctor or contact the team directly.
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Studies of the drugs tested here: Ibuzatrelvir · Remdesivir