This study is designed to understand how a medicine called tenapanor and its byproduct AZ13792925 are present in the breast milk of women who are breastfeeding. Pharmacokinetics (PK) means studying how the body processes a drug, including how it is absorbed, distributed, and eliminated. The study will last for 10 days. Participants will take tenapanor for 4 days, and their breast milk will be collected at specific times on the last day to measure drug levels. After taking tenapanor, mothers cannot feed this milk to their babies for 72 hours.

• Participants need to visit the study site for screening, dosing, and follow-up visits.
• Participants must be healthy, breastfeeding for at least 4 weeks, and not planning to wean soon.
• Breast milk collected during the study cannot be fed to infants.