A Study to Evaluate Vonoprazan Concentrations in Breast Milk of Healthy Lactating Women Receiving Vonoprazan 20 mg Once Daily or Vonoprazan 20 mg Twice Daily

Inclusion Criteria:

1. The participant is a healthy lactating woman at least 18 years of age at the time ofsigning the informed consent form (ICF).

2. The participant has delivered a normal term infant (at least 37 weeks gestation) andhas been breastfeeding or actively pumping breast milk for at least 4 weekspostpartum prior to the first dose.

3. The participant is willing to not breastfeed or otherwise use her breast milk duringadministration of vonoprazan and until at least 5 days after the last dose of thestudy drug.

4. The participant has confirmed that her breastfed infant is able to feed from abottle.

5. The participant agrees to collect all breast milk from pre-dose to 24 hours afterthe morning dose administration on Day 4, using an electric pump.

6. The participant is considered by the investigator to be in good general health asdetermined by medical history, clinical laboratory test results, vital signmeasurements, 12-lead ECG results, and physical examination findings at Screening.

7. Participants of childbearing potential must use an acceptable method of birthcontrol (ie, diaphragm with spermicide, intrauterine device, condom with foam orvaginal spermicide, oral contraceptives, or abstinence) or be surgically sterile (ie, hysterectomy, bilateral tubal ligation, or bilateral oophorectomy). Allparticipants must have a negative pregnancy test at Screening and before the firstdose of study drug (Baseline).

8. The participant agrees to comply with all protocol requirements.

9. The participant is able to provide written informed consent.

Exclusion Criteria:

1. The participant has a positive pregnancy test at Screening or Baseline, is planningto become pregnant before, during, or within 4 weeks after participating in thisstudy, or intends to donate ova during this time period, or is of childbearingpotential and not using an effective contraceptive method.

2. The participant has a history of breast implants, breast augmentation, or breastreduction surgery that significantly impacts breastfeeding or collection of milkfrom one or both breasts.

3. The participant has signs or symptoms of mastitis or other condition that wouldprevent the collection of milk from one or both breasts.

4. The participant has undergone prior esophageal and/or gastrointestinal surgeriesthat may affect study drug absorption.

5. The participant has undergone surgery (other than cesarean section) within 30 daysbefore the first dose of study drug.

6. The participant has a positive test result for hepatitis B surface antigen,hepatitis C virus antibody, or human immunodeficiency virus types 1 or 2 antibodiesat Screening.

7. The participant has any other clinically significant findings on physicalexamination, clinical laboratory abnormalities, or ECG results that precludeparticipation in the study, as deemed by the investigator.

8. The participant has used any prescription (excluding hormonal birth control) and/orover-the-counter medications (including cytochrome P450 3A4 inducers), includingherbal or nutritional supplements, within 14 days before the first dose of studydrug, and/or is expected to require any such medication during the course of thestudy until end of the Treatment Period. Use of multivitamins and acetaminophen (upto 2 g per day) is permissible.

9. The participant has consumed grapefruit and/or grapefruit juice, Seville orange, orSeville orange-containing products (eg, marmalade) within 7 days before the firstdose of study drug and/or is expected to be unable to abstain through the study.

10. The participant is a smoker or has used nicotine or nicotine-containing products (eg, snuff, nicotine patch, nicotine chewing gum, mock cigarettes, or inhalers)within 6 months before the first dose of study drug.

11. The participant has a history of alcohol abuse or drug dependency within 12 monthsbefore the first dose of study drug.

12. The participant has a positive test result for drugs of abuse, alcohol, or cotinine (indicating active current smoking) at Screening, Baseline, or Day 4 (Check-in).

13. The participant is involved in strenuous activity or contact sports within 24 hoursbefore the first dose of study drug and during the study.

14. The participant has a history of relevant drug and/or food allergies (ie, anysignificant food allergy that could preclude a standard diet in the clinicalresearch unit).

15. The participant has received study drug in another investigational study (includingvonoprazan) within 30 days prior to start of the Screening Period.

16. The participant has a history of hypersensitivity or allergies to vonoprazan or anyof its formulation excipients (D-mannitol, microcrystalline cellulose, hydroxypropylcellulose, fumaric acid, ascorbic acid, croscarmellose sodium, magnesium stearate,hypromellose, polyethylene glycol 8000, titanium dioxide, or ferric oxide red).

17. In the opinion of the investigator, the participant is not suitable for entry intothe study.