A Study to Learn About the Study Medicine (Nirmatrelvir Plus Ritonavir) in Pregnant Women With COVID-19

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:

• 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 Overview

• Status: Terminated
• Conditions: COVID-19
• Intervention / Treatment: Drug: nirmatrelvir; Drug: ritonavir

• Study Type: Interventional
• Enrollment (Actual): 25
• Phase: Phase 1

Contacts and Locations

Study Locations

• United States
  • Alabama
    • Birmingham, Alabama, United States, 35233
      • University of Alabama at Birmingham/Center for Women's Reproductive Health
  • Florida
    • Cutler Bay, Florida, United States, 33157
      • Beautiful Minds Clinical Research Center
    • DeBary, Florida, United States, 32713
      • Omega Research DeBary
    • Orlando, Florida, United States, 32808
      • Omega Research Orlando
    • Tampa, Florida, United States, 33615
      • Santos Research Center
  • Idaho
    • Idaho Falls, Idaho, United States, 83404
      • Clinical Research Prime
  • Montana
    • Missoula, Montana, United States, 59804
      • Boeson Research MSO
    • Missoula, Montana, United States, 59804
      • Origin Health
  • Texas
    • League City, Texas, United States, 77573
      • Maximos Ob/Gyn
  • Utah
    • Salt Lake City, Utah, United States, 84108
      • University of Utah
    • Salt Lake City, Utah, United States, 84112
      • University of Utah
    • Salt Lake City, Utah, United States, 84132
      • University of Utah Hospital
    • Salt Lake City, Utah, United States, 84132
      • University of Utah Clinical Neuroscience Center

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 50 years (Adult)
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• 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

Exclusion Criteria:

• 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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Non-Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Cohort 1; Pregnant women in their second trimester	Drug: nirmatrelvir; Nirmatrelvir (tablets) administered by mouth every 12 hours for 5 days (10 doses total); Other Names: PF-07321332; Drug: ritonavir; Ritonavir (capsules) administered by mouth every 12 hours for 5 days (10 doses total)
Experimental: Cohort 2; Pregnant women in their third trimester	Drug: nirmatrelvir; Nirmatrelvir (tablets) administered by mouth every 12 hours for 5 days (10 doses total); Other Names: PF-07321332; Drug: ritonavir; Ritonavir (capsules) administered by mouth every 12 hours for 5 days (10 doses total)
Experimental: Cohort 3; Non-pregnant women	Drug: nirmatrelvir; Nirmatrelvir (tablets) administered by mouth every 12 hours for 5 days (10 doses total); Other Names: PF-07321332; Drug: ritonavir; Ritonavir (capsules) administered by mouth every 12 hours for 5 days (10 doses total)

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Apparent Oral Clearance (CL/F)	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)	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)	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)	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)	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)	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)	Baseline up through Day 34
Incidence of TEAEs, SAEs, and AEs leading to discontinuations	Baseline up through end of treatment (Day 5/Day 6)

Secondary Outcome Measures

Outcome Measure	Time Frame
Number of participants with delivery at medical facility	At delivery of the baby
Number of participants with delivery at home	At delivery of the baby
Number of participants with delivery at other location	At delivery of the baby
Number of participants with caesarean section delivery	At delivery of the baby
Number of participants with vaginal delivery	At delivery of the baby
Number of participants with complications during delivery	At delivery of the baby
Number of full-term live deliveries	At delivery of the baby
Number of premature live deliveries	At delivery of the baby
Number of participants with stillbirths	At delivery of the baby
Number of participants with spontaneous abortions	At delivery of the baby
Number of participants with induced/elective abortions	At delivery of the baby
Number of participants with unknown delivery	At delivery of the baby
Number of aborted or stillborn fetuses with abnormal findings upon gross visual inspection	At delivery of the baby
Gestational age of newborn infants	At birth
Number of neonates with congenital malformation/anomaly or other neonatal problem	At birth
Body weight of newborn infants	At birth
Body length of newborn infants	At birth
Head circumference of newborn infants	At birth
Incidence of SAEs in newborn infants	Birth through 24 hours after birth or until Study Day 34 (whichever is later)

Collaborators and Investigators

• Sponsor: Pfizer
• Investigators: Study Director: Pfizer CT.gov Call Center, Pfizer

Publications and helpful links

Helpful Links

• To obtain contact information for a study center near you, click here.

Study record dates

Study Major Dates

• Study Start (Actual): June 22, 2022
• Primary Completion (Actual): March 26, 2025
• Study Completion (Actual): May 12, 2025

Study Registration Dates

• First Submitted: May 20, 2022
• First Submitted That Met QC Criteria: May 20, 2022
• First Posted (Actual): May 23, 2022

Study Record Updates

• Last Update Posted (Actual): July 29, 2025
• Last Update Submitted That Met QC Criteria: July 24, 2025
• Last Verified: July 1, 2025

More Information

Terms related to this study

• Keywords: Pregnancy; Severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2); Paxlovid; Nirmatrelvir
• Additional Relevant MeSH Terms: Respiratory Tract Infections; Infections; RNA Virus Infections; Virus Diseases; Respiratory Tract Diseases; Lung Diseases; Pneumonia, Viral; Pneumonia; Coronavirus Infections; Coronaviridae Infections; Nidovirales Infections; COVID-19; Viral Protease Inhibitors; Anti-Infective Agents; Molecular Mechanisms of Pharmacological Action; Protease Inhibitors; Enzyme Inhibitors; Antiviral Agents; Cytochrome P-450 Enzyme Inhibitors; Anti-HIV Agents; Anti-Retroviral Agents; HIV Protease Inhibitors; Cytochrome P-450 CYP3A Inhibitors; Nirmatrelvir; Ritonavir
• Other Study ID Numbers: C4671035; NCT05386472 (Registry Identifier: ClinicalTrials.gov)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: 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.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No