A Study to Learn About the Medicine (PF-07321332 or Nirmatrelvir/Ritonavir) in Healthy Lactating Women

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Status and phase

Phase 1


Healthy Participants


Drug: ritonavir
Drug: nirmatrelvir

Study type


Funder types



2022-001020-15 (EudraCT Number)

Details and patient eligibility


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.


8 patients




18 to 55 years old


Accepts Healthy Volunteers

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

Trial design

Primary purpose




Interventional model

Single Group Assignment


None (Open label)

8 participants in 1 patient group

Experimental group
nirmatrelvir/ritonavir will be given by mouth two times a day as a tablet
Drug: nirmatrelvir
Drug: ritonavir

Trial contacts and locations



Central trial contact

Pfizer CT.gov Call Center

Data sourced from clinicaltrials.gov

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