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Small study tests COVID pill levels in breast milk

NCT ID NCT05441215

Knowledge-focused Sponsor: Pfizer Source: ClinicalTrials.gov ↗

What the study statuses mean

This study's is highlighted.

Recruitment status, easiest to join first

Recruiting now
This trial is taking on new participants right now.
Not yet recruiting
Registered, but not yet taking participants.
By invitation only
Not open to general applications. Only people the study team invites can take part.
Paused
Paused for now. It may or may not start again.
Ongoing
Running, but no longer taking on new participants.
Completed This study
The trial has finished. Results may not be published yet.
Stopped early
Stopped early, before it reached the end. That can be for many reasons, including safety.
Cancelled
Cancelled before anyone took part.

Expanded access (not trials)

Expanded access
Not a trial. This treatment can be requested outside a study, case by case, for people who qualify.
Expanded access (paused)
Not a trial. The treatment can normally be requested outside a study, but is unavailable right now.
Expanded access (ended)
Not a trial. The treatment could once be requested outside a study, but no longer can.
Approved
The treatment has been approved, so it is available normally rather than through this programme.

When the status isn't known

Details not published
The full record has not been published yet, so there is little to show here.
Status unknown
This status has not been confirmed recently, so it may be out of date.

First seen Jun 24, 2026 · Last updated Jun 27, 2026 · Updated 1 time

Summary

This completed Phase 1 study looked at how much of the COVID-19 treatment nirmatrelvir/ritonavir (Paxlovid) gets into breast milk. Eight healthy breastfeeding women took the drug by mouth three times over two days. Researchers collected breast milk samples to measure drug levels, aiming to provide safety information for nursing mothers.

What this could mean

Our plain-language read of the trial. This is informational only, not medical advice or a prediction.

Active substance
nirmatrelvir/ritonavir (Paxlovid)
What this could lead to
If successful, this study could help doctors understand whether nirmatrelvir/ritonavir is safe for breastfeeding women and their infants.
What could go wrong
This is a very small, early-phase study with only 8 participants. It measures drug levels in breast milk, not safety or effectiveness in treating illness.

This is an AI summary of the original study and may miss details. Read our disclaimer.

Study facts

What this study's own registry entry says, in plain language.

Phase

Phase 1

The first testing in people. Mainly checks safety and dose, usually in a small group.

Participants

8 people

The number who actually took part.

Started

Dec 2022

Finished

Dec 2023

Lead sponsor

A company

The lead sponsor is a pharmaceutical, biotech, or medical-device company.

Who can take part

This study's own entry requirements. Only the study team can say for certain whether you qualify.

Ages

18 to 55 years

Sex

Female participants only

Healthy volunteers

Accepted

You do not need to have the condition being studied to take part.

Show the full entry requirements

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

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

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Conditions

The condition(s) this trial relates to.

Breast Feeding COVID-19

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

Healthy participants

Contacts and locations

Locations

  • Pfizer Clinical Research Unit - Brussels

    Brussels, Bruxelles-capitale, Région de, B-1070, Belgium

More trials for these conditions

Other studies related to the condition(s) this trial covers.