COVID-19Phase 1NCT05386472
A Study to Learn About the Study Medicine (Nirmatrelvir Plus Ritonavir) in Pregnant Women With COVID-19
A Phase 1 study testing nirmatrelvir and ritonavir in people with COVID-19, run by Pfizer at 13 sites in United States.
Trial summary
The purpose of this clinical trial is to learn about how study medicine (Paxlovid, which contains nirmatrelvir and ritonavir) is changed and eliminated from the body, as well as its safety, and the extent to which side effects can be tolerated for treatment of pregnant women with mild or moderate COVID-19 compared to… Read more about this study
- Who is it for?
- Ages 18 to 50 years, women only
- Conditions the study is for
- COVID-19
- What is being tested?
- nirmatrelvir and ritonavir
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 25 participants
- Where
- 13 sitesUnited States
- Study dates
- 22 Jun 2022to 13 May 2025
- Phase
- Phase 1
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 50 years
- Women only
- No healthy volunteers
- Adult
Who may be able to join
- All cohorts: Mild-to-moderate COVID-19 infection confirmed in sample collected ≤5 days prior to enrollment; onset within 5 days prior to enrollment and presence of ≥1 sign/symptom on the day of enrollment.
- Cohorts 1\&2: Expecting single baby; Pregnant in 2nd trimester, 14 0/7 to 27 6/7 weeks of gestational age (Cohort 1) or 3rd trimester, ≥28 0/7 and ≤34 6/7 weeks of gestational age (Cohort 2), by ultrasound.
- All cohorts: Otherwise healthy participants who are determined by medical history, physical examination, and clinical judgment to be appropriate for inclusion in the study
Who cannot join
- All cohorts: Current need for hospitalization or anticipated need for hospitalization in the clinical opinion of the site investigator.
- Cohorts 1\&2: Prior/current major condition or illness of mother/fetus substantially increasing risk of study participation/completion or impacting pregnancy/fetal outcomes in investigator's judgement.
- All cohorts: Current use of any medications that are highly dependent on CYP3A4 for clearance, and which are contraindicated in combination with nirmatrelvir/ritonavir.
- All cohorts: Has received or is expected to receive monoclonal antibody treatment, convalescent COVID-19 plasma, or anti-viral treatment (eg, molnupiravir) for the current SARSCoV-2 infection.
- All cohorts: Participants with moderate to severe kidney impairment
Trial locations and contacts
13 sites in 1 country.
13 sites in 1 country
United States13 sites
University of Alabama at Birmingham/Center for Women's Reproductive Health
Birmingham, Alabama, 35233
Beautiful Minds Clinical Research Center
Cutler Bay, Florida, 33157
Omega Research Debary
DeBary, Florida, 32713
Clinical Research Prime
Idaho Falls, Idaho, 83404
Maximos Ob/Gyn
League City, Texas, 77573
Boeson Research MSO
Missoula, Montana, 59804
Origin Health
Missoula, Montana, 59804
Omega Research Orlando
Orlando, Florida, 32808
University of Utah
Salt Lake City, Utah, 84108
University of Utah
Salt Lake City, Utah, 84112
University of Utah Clinical Neuroscience Center
Salt Lake City, Utah, 84132
University of Utah Hospital
Salt Lake City, Utah, 84132
Santos Research Center
Tampa, Florida, 33615
About this study
Official title: A PHASE 1, OPEN-LABEL STUDY TO EVALUATE THE PHARMACOKINETICS, SAFETY, AND TOLERABILITY OF ORALLY ADMINISTERED NIRMATRELVIR/RITONAVIR IN PREGNANT WOMEN WITH MILD-TO-MODERATE COVID-19
The purpose of this clinical trial is to learn about how study medicine (Paxlovid, which contains nirmatrelvir and ritonavir) is changed and eliminated from the body, as well as its safety, and the extent to which side effects can be tolerated for treatment of pregnant women with mild or moderate COVID-19 compared to non-pregnant women with mild or moderate COVID-19.
This study is seeking participants who:
Read more
- are expecting a healthy baby and are in their second or third trimester pregnancy and have mild or moderate COVID-19
- are not pregnant and have mild or moderate COVID-19.
All participants in this study will take Paxlovid by mouth every 12 hours for 5 days. We will study the experiences of people receiving the study medicine. This will help us decide if the study medicine is safe.
All participants will take part in this study for at least 34 days; pregnant participants will take part until their delivery, so that the study duration may be up to 6 months, depending on their delivery date.
During this time, participants will have 7to 8 visits and, if pregnant, a visit at delivery. Around 2 to 3 visits and the delivery visit will be done in person (at the clinic or at the participant's home). The other 5 visits may be done over the phone, unless in-person visit is necessary as decided by the doctor. Blood samples will be collected on the first 4 to 5 study visits (and at other study visits, if necessary).
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
nirmatrelvirDrug
Also called PF-07321332
Nirmatrelvir (tablets) administered by mouth every 12 hours for 5 days (10 doses total)
ritonavirDrug
Ritonavir (capsules) administered by mouth every 12 hours for 5 days (10 doses total)
| Study group | Role | What they receive |
|---|---|---|
| Cohort 1 | Experimental | Pregnant women in their second trimester Receives: Drug: nirmatrelvir; Drug: ritonavir |
| Cohort 2 | Experimental | Pregnant women in their third trimester Receives: Drug: nirmatrelvir; Drug: ritonavir |
| Cohort 3 | Experimental | Non-pregnant women Receives: Drug: nirmatrelvir; Drug: ritonavir |
What is being measured
The primary outcome is the main question the study is designed to answer.
Apparent Oral Clearance (CL/F)
Measured: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Apparent Volume of Distribution (Vz/F)
Measured: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Area Under the Curve From Time Zero to End of Dosing Interval (AUCtau)
Measured: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Maximum Observed Plasma Concentration (Cmax)
Measured: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Plasma Decay Half-Life (t1/2)
Measured: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Observed Plasma Trough Concentration (Ctrough)
Measured: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Incidence of Treatment Emergent Adverse Events (TEAEs)
Measured: Baseline up through Day 34
Incidence of TEAEs, SAEs, and AEs leading to discontinuations
Measured: Baseline up through end of treatment (Day 5/Day 6)
Secondary outcomes (19)
Number of participants with delivery at medical facility
Measured: At delivery of the baby
Number of participants with delivery at home
Measured: At delivery of the baby
Number of participants with delivery at other location
Measured: At delivery of the baby
Number of participants with caesarean section delivery
Measured: At delivery of the baby
Number of participants with vaginal delivery
Measured: At delivery of the baby
Number of participants with complications during delivery
Measured: At delivery of the baby
Number of full-term live deliveries
Measured: At delivery of the baby
Number of premature live deliveries
Measured: At delivery of the baby
Number of participants with stillbirths
Measured: At delivery of the baby
Number of participants with spontaneous abortions
Measured: At delivery of the baby
Number of participants with induced/elective abortions
Measured: At delivery of the baby
Number of participants with unknown delivery
Measured: At delivery of the baby
Number of aborted or stillborn fetuses with abnormal findings upon gross visual inspection
Measured: At delivery of the baby
Gestational age of newborn infants
Measured: At birth
Number of neonates with congenital malformation/anomaly or other neonatal problem
Measured: At birth
Body weight of newborn infants
Measured: At birth
Body length of newborn infants
Measured: At birth
Head circumference of newborn infants
Measured: At birth
Incidence of SAEs in newborn infants
Measured: Birth through 24 hours after birth or until Study Day 34 (whichever is later)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted23 May 2022
- Study start22 Jun 2022
- Primary completion26 Mar 2025
- Study completion13 May 2025
Why it stopped: The trial prematurely terminated due to the inability to recruit the planned number of subjects. The decision to terminate the trial was not based on any safety concerns.
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for COVID-19Studies of the same condition, open and under way.
- More trials run by PfizerThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 1
- Primary purpose
- Treatment
- Allocation
- Non-randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Enrolment
- 25 participants (actual)
Sponsor and investigators
- Lead sponsor
- Pfizer
- Sponsor type
- Industry (pharma, biotech, devices)
- Responsible party
- Sponsor
- Investigators
- Pfizer CT.gov Call Center, Study director, Pfizer
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT05386472
- Sponsor's protocol ID
- C4671035
- Other IDs
- NCT05386472
- Status last verified
- Aug 2026
- First submitted
- 20 May 2022
- Last updated
- 17 Aug 2026
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- Yes
- FDA-regulated device
- No
- Individual data sharing
- No: 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.
Study at a glance
From the registry record, last updated by the sponsor on 17 Aug 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- A PHASE 1, OPEN-LABEL STUDY TO EVALUATE THE PHARMACOKINETICS, SAFETY, AND TOLERABILITY OF ORALLY ADMINISTERED NIRMATRELVIR/RITONAVIR IN PREGNANT WOMEN WITH MILD-TO-MODERATE COVID-19
- ClinicalTrials.gov ID
- NCT05386472
- Acronym / sponsor ID
- C4671035
- Conditions
- COVID-19
- Keywords
- Severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2), Pregnancy, Paxlovid, Nirmatrelvir
- Phase
- Phase 1
- Study type
- Interventional
- Recruitment status
- TerminatedReason stopped: The trial prematurely terminated due to the inability to recruit the planned number of subjects. The decision to terminate the trial was not based on any safety concerns.
- Enrolment
- 25 participants (actual)
- Lead sponsor
- PfizerIndustry (pharma, biotech, devices)
- Study start
- 22 Jun 2022 (actual)
- Primary completion
- 26 Mar 2025 (actual)
- Study completion
- 13 May 2025 (actual)
- First posted
- 23 May 2022 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
The purpose of this clinical trial is to learn about how study medicine (Paxlovid, which contains nirmatrelvir and ritonavir) is changed and eliminated from the body, as well as its safety, and the extent to which side effects can be tolerated for treatment of pregnant women with mild or moderate COVID-19 compared to non-pregnant women with mild or moderate COVID-19.
This study is seeking participants who:
- are expecting a healthy baby and are in their second or third trimester pregnancy and have mild or moderate COVID-19
- are not pregnant and have mild or moderate COVID-19.
All participants in this study will take Paxlovid by mouth every 12 hours for 5 days. We will study the experiences of people receiving the study medicine. This will help us decide if the study medicine is safe.
All participants will take part in this study for at least 34 days; pregnant participants will take part until their delivery, so that the study duration may be up to 6 months, depending on their delivery date.
During this time, participants will have 7to 8 visits and, if pregnant, a visit at delivery. Around 2 to 3 visits and the delivery visit will be done in person (at the clinic or at the participant's home). The other 5 visits may be done over the phone, unless in-person visit is necessary as decided by the doctor. Blood samples will be collected on the first 4 to 5 study visits (and at other study visits, if necessary).
Study design
- Primary purpose
- Treatment
- Allocation
- Non-randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Number of arms
- 3
| Arm | Type | Receives |
|---|---|---|
| Cohort 1 | Experimental | Drug: nirmatrelvir, Drug: ritonavirPregnant women in their second trimester |
| Cohort 2 | Experimental | Drug: nirmatrelvir, Drug: ritonavirPregnant women in their third trimester |
| Cohort 3 | Experimental | Drug: nirmatrelvir, Drug: ritonavirNon-pregnant women |
Who may qualify
- Ages
- 18 to 50 years
- Sex
- Female only
- Healthy volunteers
- Not accepted
- Age groups
- Adult
Key inclusion criteria (3 listed)
- All cohorts: Mild-to-moderate COVID-19 infection confirmed in sample collected ≤5 days prior to enrollment; onset within 5 days prior to enrollment and presence of ≥1 sign/symptom on the day of enrollment.
- Cohorts 1\&2: Expecting single baby; Pregnant in 2nd trimester, 14 0/7 to 27 6/7 weeks of gestational age (Cohort 1) or 3rd trimester, ≥28 0/7 and ≤34 6/7 weeks of gestational age (Cohort 2), by ultrasound.
- All cohorts: Otherwise healthy participants who are determined by medical history, physical examination, and clinical judgment to be appropriate for inclusion in the study
Key exclusion criteria (5 listed)
- All cohorts: Current need for hospitalization or anticipated need for hospitalization in the clinical opinion of the site investigator.
- Cohorts 1\&2: Prior/current major condition or illness of mother/fetus substantially increasing risk of study participation/completion or impacting pregnancy/fetal outcomes in investigator's judgement.
- All cohorts: Current use of any medications that are highly dependent on CYP3A4 for clearance, and which are contraindicated in combination with nirmatrelvir/ritonavir.
- All cohorts: Has received or is expected to receive monoclonal antibody treatment, convalescent COVID-19 plasma, or anti-viral treatment (eg, molnupiravir) for the current SARSCoV-2 infection.
- All cohorts: Participants with moderate to severe kidney impairment
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| nirmatrelvirAlso: PF-07321332Nirmatrelvir (tablets) administered by mouth every 12 hours for 5 days (10 doses total) | Drug | Cohort 1, Cohort 2, Cohort 3 |
| ritonavirRitonavir (capsules) administered by mouth every 12 hours for 5 days (10 doses total) | Drug | Cohort 1, Cohort 2, Cohort 3 |
Primary outcome
Apparent Oral Clearance (CL/F)
Time frame: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Apparent Volume of Distribution (Vz/F)
Time frame: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Area Under the Curve From Time Zero to End of Dosing Interval (AUCtau)
Time frame: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Maximum Observed Plasma Concentration (Cmax)
Time frame: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Plasma Decay Half-Life (t1/2)
Time frame: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Observed Plasma Trough Concentration (Ctrough)
Time frame: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.
Incidence of Treatment Emergent Adverse Events (TEAEs)
Time frame: Baseline up through Day 34
Incidence of TEAEs, SAEs, and AEs leading to discontinuations
Time frame: Baseline up through end of treatment (Day 5/Day 6)
19 secondary outcomes
Number of participants with delivery at medical facility
Time frame: At delivery of the baby
Number of participants with delivery at home
Time frame: At delivery of the baby
Number of participants with delivery at other location
Time frame: At delivery of the baby
Number of participants with caesarean section delivery
Time frame: At delivery of the baby
Number of participants with vaginal delivery
Time frame: At delivery of the baby
Number of participants with complications during delivery
Time frame: At delivery of the baby
Number of full-term live deliveries
Time frame: At delivery of the baby
Number of premature live deliveries
Time frame: At delivery of the baby
Number of participants with stillbirths
Time frame: At delivery of the baby
Number of participants with spontaneous abortions
Time frame: At delivery of the baby
Number of participants with induced/elective abortions
Time frame: At delivery of the baby
Number of participants with unknown delivery
Time frame: At delivery of the baby
Number of aborted or stillborn fetuses with abnormal findings upon gross visual inspection
Time frame: At delivery of the baby
Gestational age of newborn infants
Time frame: At birth
Number of neonates with congenital malformation/anomaly or other neonatal problem
Time frame: At birth
Body weight of newborn infants
Time frame: At birth
Body length of newborn infants
Time frame: At birth
Head circumference of newborn infants
Time frame: At birth
Incidence of SAEs in newborn infants
Time frame: Birth through 24 hours after birth or until Study Day 34 (whichever is later)
Results and safety
The study was stopped early (reason given: The trial prematurely terminated due to the inability to recruit the planned number of subjects. The decision to terminate the trial was not based on any safety concerns.). Results are not available in the source record.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 17 Aug 2026.
- To obtain contact information for a study center near you, click here.Link provided by the sponsor.
- Individual participant dataSharing planned: No. 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.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Pfizer CT.gov Call Center study director
Pfizer
13 sites in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 1 study testing nirmatrelvir and ritonavir in people with COVID-19, run by Pfizer at 13 sites in United States.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 3 inclusion and 5 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: stopped early, as of the sponsor's last update on 17 Aug 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 13 sites in United States. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this phase mean?
Phase 1 studies test a treatment in a small group of people for the first time or in a new way, mainly to check safety and find the right dose.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
The study was stopped early (reason given: The trial prematurely terminated due to the inability to recruit the planned number of subjects. The decision to terminate the trial was not based on any safety concerns.). Results are not available in the source record.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Apparent Oral Clearance (CL/F) (time frame: Day 1: 1-3 hour post-dose; Day 3: 4-8 hour post-dose; Day 4: 8 to less than 12 hour post dose; Day 5: 2-4 hour, 6-8 hour, 10 to less than 12 hour post dose.). The study lists 8 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 17 Aug 2026.