Phase 1
Completed N=8
A Study to Learn About the Medicine (PF-07321332 or Nirmatrelvir/Ritonavir) in Healthy Lactating Women
Healthy Participants
Source: ClinicalTrials.gov NCT05441215 ↗
Enrolled (actual)
8
Serious AEs
0.0%
Results posted
May 2026
Primary outcomePrimary: The Maximum Observed Concentration of Nirmatrelvir in Breast Milk Over the Dosing Interval — 1904 Nanograms / milliliter (ng/mL)
Summary
The main purpose of this study is to measure the level of active ingredient of the study medicine (nirmatrelvir) that is secreted in human breast milk when it is given to healthy breastfeeding women. The study medicine consists of two medicines, nirmatrelvir and ritonavir. We are seeking female participants who are:
* Actively breast-feeding (lactating) at least 12 weeks postpartum;
* Age between 18 to 55 years and not currently pregnant;
* Have a Body Mass Index (BMI): 17.5 kg/m2; and a total body weight >50 kg (110 lb).
Participants will take the study medicine by mouth for a total of 3 times over 2 days (2 morning doses and 1 evening dose) at the study clinic. We will periodically collect breast milk from day 2 to 4 to measure the level of nirmatrelvir and ritonavir in it. A safety follow up call will be conducted around 28-35 days from the last dose to monitor any reactions participants may have to the study medicine.
Outcome Measures
| Outcome | Result | p-value |
|---|---|---|
| PRIMARY The Maximum Observed Concentration of Nirmatrelvir in Breast Milk Over the Dosing Interval |
1904 | — |
| PRIMARY Time to Reach Cmax of Nirmatrelvir in Breast Milk |
3.22 | — |
| PRIMARY Area Under the Concentration-Time Profile From Time Zero to End of Dosing Interval for Nirmatrelvir in Breast Milk |
12770 | — |
| PRIMARY Terminal Half-Life of Nirmatrelvir in Breast Milk |
4.455 | — |
| PRIMARY The Average Steady State Concentration of Nirmatrelvir in Breast Milk |
1063 | — |
| PRIMARY The Amount of Nirmatrelvir Excreted in Breast Milk Over the Dosing Interval Tau |
0.3758 | — |
| PRIMARY The Percent of Amount of Nirmatrelvir Excreted in Breast Milk Over The Dosing Interval Tau |
0.1253 | — |
| PRIMARY Breast Milk Clearance of Nirmatrelvir |
0.007641 | — |
| SECONDARY The Maximum Observed Concentration of Ritonavir in Breast Milk Observed Over the Dosing Interval |
71.99 | — |
| SECONDARY Time to Reach Cmax of Ritonavir in Breast Milk |
3.17 | — |
| SECONDARY Area Under the Concentration-Time Profile for Ritonavir in Breast Milk From Time Zero to End of Dosing Interval |
456.8 | — |
| SECONDARY Half-Life of Ritonavir in Breast Milk |
NA | — |
| SECONDARY The Average Steady State Concentration of Ritonavir in Breast Milk |
38.08 | — |
| SECONDARY The Amount of Ritonavir Excreted in Breast Milk Over the Dosing Interval Tau |
0.01354 | — |
| SECONDARY The Percent of Ritonavir Excreted in Breast Milk Over The Dosing Interval Tau |
0.01354 | — |
| SECONDARY Breast Milk Clearance of Ritonavir |
0.001966 | — |
| SECONDARY The Maximum Observed Concentration of Nirmatrelvir in Plasma Observed Over the Dosing Interval |
7080 | — |
| SECONDARY The Maximum Observed Concentration of Ritonavir in Plasma Observed Over the Dosing Interval |
1228 | — |
| SECONDARY Area Under the Concentration-Time Profile for Nirmatrelvir in Plasma From Time Zero to End of Dosing Interval |
49190 | — |
| SECONDARY Area Under the Concentration-Time Profile for Ritonavir in Plasma From Time Zero to End of Dosing Interval |
6893 | — |
| SECONDARY Half-Life of Nirmatrelvir in Plasma |
7.180 | — |
| SECONDARY Half-Life of Ritonavir in Plasma |
5.190 | — |
| SECONDARY The Minimum Plasma Concentration of Nirmatrelvir Observed Over the Dosing Interval |
1240 | — |
| SECONDARY The Minimum Plasma Concentration of Ritonavir Observed Over the Dosing Interval |
136.9 | — |
| SECONDARY Time to Reach Cmax of Nirmatrelvir in Plasma |
3.56 | — |
| SECONDARY Time to Reach Cmax of Ritonavir in Plasma |
4.03 | — |
| SECONDARY Apparent Clearance of Nirmatrelvir From Plasma |
6.099 | — |
| SECONDARY Apparent Clearance of Ritonavir From Plasma |
14.50 | — |
| SECONDARY Apparent Volume of Nirmatrelvir Distribution |
62.16 | — |
| SECONDARY Apparent Volume of Ritonavir Distribution |
107.5 | — |
| SECONDARY The Average Steady State Concentration of Nirmatrelvir in Plasma |
4098 | — |
| SECONDARY The Average Steady State Concentration of Ritonavir in Plasma |
574.5 | — |
| SECONDARY Daily (24 Hour) Amount of Nirmatrelvir Excreted in Breast Milk |
0.7520 | — |
| SECONDARY Daily (24 Hour) Amount of Ritonavir Excreted in Breast Milk |
0.02709 | — |
| SECONDARY Milk to Plasma Ratio of Nirmatrelvir for AUCtau During Dosing Interval |
0.2596 | — |
| SECONDARY Milk to Plasma Ratio of Ritonavir for AUCtau During Dosing Interval |
0.06626 | — |
| SECONDARY Milk to Plasma Ratio of Nirmatrelvir for Cmax During Dosing Interval |
0.2689 | — |
| SECONDARY Milk to Plasma Ratio of Ritonavir for Cmax During Dosing Interval |
0.05860 | — |
| SECONDARY Body Weight Normalized Infant Dose (BWNID) of Nirmatrelvir in mg/kg/Day |
0.1595 | — |
| SECONDARY BWNID of Ritonavir in mg/kg/Day |
0.005709 | — |
| SECONDARY Body Weight Normalized Maternal Dose (BWNMD) of Nirmatrelvir in mg/kg/Day |
8.969 | — |
| SECONDARY BWNMD of Ritonavir in mg/kg/Day |
2.990 | — |
| SECONDARY Infant Dose Expressed As % of Body Weight Normalized Maternal Dose (BWNIDPCM) for Nirmatrelvir |
1.779 | — |
| SECONDARY BWNIDPCM for Ritonavir |
0.1910 | — |
| SECONDARY Number of Participants With Treatment Emergent Adverse Events |
8 | — |
| SECONDARY Number of Participants With Laboratory Abnormalities (Without Regard to Baseline Abnormality) |
1; 1; 3 | — |
| SECONDARY Number of Participants With Vital Signs Abnormalities |
1 | — |
| SECONDARY Number of Participants With ECG Abnormalities |
— | — |
| SECONDARY Number of Participants With Physical Examination Abnormalities |
— | — |
Eligibility Criteria
Inclusion Criteria
- Healthy lactating females who are actively breast-feeding or expressing breast milk, at least 12 weeks post-partum and not currently pregnant between 18 and 55 years old
- Body Mass Index (BMI): 17.5 kg/m2; and a total body weight >50 kg (110 lb)
- Infants of women enrolled in the study must be able to feed successfully from a bottle or other age-appropriate alternative feeding method prior to the start of the study and must be able to tolerate infant formula if the mother does not have a supply of stored breast milk sufficient to cover the duration of the study
- Participants must be willing to temporarily discontinue breast feeding their infants for a total of 4.5 days (108 hours)
- Participants must be willing to regularly pump breasts throughout the study and express milk according to a schedule designed to maintain lactation throughout the study period
Exclusion Criteria
- Positive test result (RT-PCR) for SARS-CoV-2 infection at the time of screening or Day -1
- Evidence or history of clinically significant findings
- History of febrile illness or mastitis within 5 days prior to the first dose of study medication
- Participants who have received a COVID-19 vaccine within 7 days before screening or admission, or who are to be vaccinated with a COVID-19 vaccine at any time during the study confinement period
- History of HIV infection, hepatitis B, or hepatitis C; positive testing for HIV, HBsAg, or HCVAb. Hepatitis B vaccination is allowed
- Abnormal vital signs such as blood pressure, 12-lead electrocardiogram
- History of alcohol abuse and/or illicit drug use, tobacco use in excess of 5 cigarettes/day or 2 chews/day
- Blood donation within 60 days
Data sourced from ClinicalTrials.gov (NCT05441215). Outcome figures and adverse-event rates are extracted automatically from the registry's posted results and are provided for clinician reference, not as a substitute for the primary publication. Informational only — not medical advice.