New gold standard for medicine safety during breastfeeding

Women who choose to stop treatments during pregnancy and breastfeeding are putting their health at risk, and have to weigh their desire to have children and breastfeed against a risk that we know very little about. In two ongoing clinical trials, researchers have established a new standard for human lactation studies that includes sampling of breast milk and plasma from both mothers and breastfed infants.

"The lack of scientific evidence is an ethical problem for women and doctors, considering that around 70% of women need to use medicines sometime during their pregnancy. In many cases, women are recommended to refrain from breastfeeding or stop using their medicines. However, breastfeeding has benefits for both mother and child," says Mats G. Hansson, senior professor of biomedical ethics, Uppsala University's Center for Research Ethics & Bioethics, head of two ongoing clinical trials.

Ninety-five percent of all medicines have not been studied well enough to include safety information for pregnancy and breastfeeding on the label. The current standard for lactation studies uses animal data and concentrations of medicines in mother's milk, using PB/PK to estimate how much of a particular substance transfers to the baby. The studies that exist are old and rely on data from very few individuals, with old analysis methods.

BMJ Open has just published a protocol for a new gold standard for clinical lactation studies, looking at the concentration of prednisolone in the mother's milk, and plasma from both mother and infant. Prednisolone is prescribed for several conditions, including rheumatoid arthritis, a chronic and debilitating condition that requires long-term treatment.

Samples are biobanked and analyzed with regard to pharmacokinetic properties of the medicines and transfer from breast milk to infant plasma. The present studies are focusing on prednisolone, used in the treatment of rheumatoid arthritis, and metformin, used in the treatment of type 2 diabetes. With biobanking and the obtainment of informed consent for future, yet unspecified research, the protocol opens for long-term follow-up of medication effects on breastfeeding infants.

Women are recruited through a network of clinical centers in Sweden, and the samples will be stored for future research in a network of breast milk biobanks managed by BBMRI-ERIC. According to Mats G. Hansson, this ensures the study is part of a larger European infrastructure, making future research possible.

The just-published protocol was developed within the large European collaboration framework ConcePTION, and describes how samples are collected and analyzed.

More information:
Jenny Svedenkrans et al, Determination of prednisolone concentration in human breast milk and plasma of breastfed infants: study protocol of a Swedish multicentre low-intervention clinical trial, BMJ Open (2025). DOI: 10.1136/bmjopen-2024-097898

Provided by Uppsala University