Medicines in Breast Milk and Estimated Infant Exposure (MedMilk)

Medication Concentrations in Human Milk (MedMilk) and Potential Adverse Effects in Breastfed Infants: an Exploratory Clinical Study

The MedMilk (Medication concentrations in human Milk) study investigates how selected medicines taken by breastfeeding women are transferred into human milk and whether this may affect the breastfed child. The study includes breastfeeding women who are already using prescription or over-the-counter medicines as part of their usual care. Participants provide samples of breast milk and urine and complete a questionnaire about maternal and infant health. The collected data will be used to quantify medicine concentrations in milk and estimate the relative infant dose. The study aims to contribute new data to support safer prescribing and more informed counselling during breastfeeding

Study Overview

• Status: Recruiting
• Conditions: Lactation; Breastfeeding; Medication Safety; Pharmacokinetic Parameters; Drug Exposure Via Breast Milk
• Intervention / Treatment: Drug: Prescription Drugs

Detailed Description

The MedMilk (Medication concentrations in human Milk) study is a prospective, exploratory clinical study coordinated by the Department of Clinical Pharmacology, Bispebjerg and Frederiksberg Hospital, Denmark. The study is observational in nature and involves no experimental drug administration. Participants are breastfeeding women using medicines as part of their routine treatment.

Each participant will provide four small breast milk samples (1-20 mL each) collected at different time points in relation to maternal drug intake, one urine sample, and questionnaire data on maternal and infant health, breastfeeding patterns, and any infant symptoms potentially related to drug exposure. Samples are stored at -80 °C in a dedicated research biobank until analysis.

Drug concentrations in milk and urine will primarily be quantified using solid Phase Extraction coupled with UPLC-MS/MS. Data will be analyzed descriptively, and relative infant doses (RID) will be calculated. For drugs with sufficient sampling density.

Results will add to the limited body of systematic data on drug transfer into human milk and help inform clinical decision-making regarding medication use during breastfeeding.

• Study Type: Observational
• Enrollment (Estimated): 250

Contacts and Locations

• Study Contact: Name: Ditte Resendal Gotfredsen, MD; Phone Number: +4521472051; Email: ditte.resendal.gotfredsen@regionh.dk
• Study Contact Backup: Name: Jon Traerup Andersen, Professor, MD, PhD; Email: jon.thor.traerup.andersen@regionh.dk

Study Locations

• Denmark
  • Copenhagen, Denmark
    • Recruiting
    • Department of Clinical Pharmacology
    • Contact: Ditte Resendal Gotfredsen, MD; Phone Number: +4521472051; Email: ditte.resendal.gotfredsen@regionh.dk
    • Contact: Jon Traerup Andersen, Professor, MD, PhD; Email: jon.thor.traerup.andersen@regionh.dk
  • Copenhagen, Denmark
    • Recruiting
    • Mental health services, Capital Region of Denmark
  • Herlev, Denmark
    • Recruiting
    • Department of Obstetrics and Gynecology, Herlev Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

• Sampling Method: Non-Probability Sample

Study Population

Participants will be lactating women recruited through obstetric, neonatal, and psychiatric departments, public health visiting nurses, and counselling services across Denmark. Recruitment will be coordinated by the Department of Clinical Pharmacology, Bispebjerg and Frederiksberg Hospital, Copenhagen. The study primarily targets women using prescription and over-the-counter medicines during breastfeeding and aims to represent real-world exposure patterns across all Danish regions.

Description

Inclusion Criteria:

• Lactating women aged ≥18 years
• Current use of one or more prescription or over-the-counter (classified within the ATC system) drugs
• Able and willing to provide written informed consent

Exclusion Criteria:

• Current pregnancy during sample collection
• Known and clinically significant pharmacokinetic drug-drug interactions at the time of sampling

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Breastfeeding women on medication	Drug: Prescription Drugs; Exposure to prescription medicines taken by breastfeeding women during routine treatment. The study does not assign medications but observes drug transfer into human milk from exposures occurring as part of usual care.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Drug concentrations in human milk	Quantification of drug concentrations in human milk, expressed in micrograms per millilitre (µg/mL). Milk samples are collected before and after the maternal dose within one dosing interval.	Within one dosing interval

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Relative Infant Dose (RID)	Estimation of infant drug exposure, expressed as the relative infant dose (% of maternal weight-adjusted dose).	Within one dosing interval
Maternal-reported infant adverse effects	Maternal questionnaire on infant symptoms potentially related to drug exposure via breastfeeding.	At the time of inclusion. Montly follow-up for three months.

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Simulated infant plasma levels	We will estimate the infant plasma level of the specific drug expressed as microgram pr. millilitre μg/ml based on pharmacokinetic modelling of infant, and drug characteristics and drug concentrations in milk samples.	During one dosing interval
Simulated Area Under the Curve (AUC)	We will estimate the 95th percentile of the pediatric Area Under the Curve (AUC) (μg x h/mL) based on pharmacokinetic modelling of infant, and drug characteristics and drug concentrations in milk samples.	During one dosing interval
Biobank establishment	Milk and urine samples stored for future pharmacokinetic analyses and secondary research	Within one dosing interval

Collaborators and Investigators

• Sponsor: University Hospital Bispebjerg and Frederiksberg
• Investigators: Principal Investigator: Jon Traerup Andersen, Professor, MD, PhD, Department of Clinical Pharmacology, Bispbjeg and Frederiksberg Hospital

Study record dates

Study Major Dates

• Study Start (Actual): December 20, 2024
• Primary Completion (Estimated): January 1, 2028
• Study Completion (Estimated): January 1, 2030

Study Registration Dates

• First Submitted: December 8, 2025
• First Submitted That Met QC Criteria: January 7, 2026
• First Posted (Estimated): January 16, 2026

Study Record Updates

• Last Update Posted (Estimated): January 16, 2026
• Last Update Submitted That Met QC Criteria: January 7, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: breastfeeding; lactation; medication safety; drug transfer into breast milk
• Additional Relevant MeSH Terms: Behavior; Feeding Behavior; Breast Feeding; Pharmaceutical Preparations; Prescription Drugs
• Other Study ID Numbers: H-23062687

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Sharing Time Frame: Study protocol, SAP and ICF after protocol publication. Analytical code and summary results after completion of data collection and analyses.
• IPD Sharing Access Criteria: Requests for data access can be directed to the principal investigator. Data sharing will require relevant approvals under Danish GDPR.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; ICF

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No