47 Determining the concentration of maternal medicines in human milk: the UmbrelLACT study protocol

Introduction An extensive information gap regarding safety of medicines during lactation still exists today. At least 50% of women need pharmacotherapy in the postpartum period and the proportion of breastfeeding women needing medication is rising, due to higher maternal age at pregnancy and increased prevalence of chronic maternal diseases, among others. Considering the lack of information, informed and shared decisions on the use of a medicine during breastfeeding are often challenging. This may result in unnecessary cessation of breastfeeding or avoidance of pharmacological treatment. The objective of UmbrelLACT, this prospective observational study, is to collect data on the human milk transfer of maternal medicines, child exposure and general health outcome of the child. In addition, we aim to evaluate the predictive performance of lactation and pediatric physiologically-based pharmacokinetic (PBPK) models. These models are an accepted approach to predict medicine exposure in special populations. Methods Breastfeeding women taking medication will be recruited via UZ Leuven, the BELpREG website and other external facilities. Each compound for which samples might be collected, will be evaluated by the team in terms of feasibility and relevance, such as societal need of data, available evidence in literature and access to an analytical assay. Participants will be asked to report clinical maternal and child variables, to collect milk samples over 24h and, optionally, to donate two blood samples (at peak and trough levels). A blood sample of the child may be collected if the parents consent. Approval of the internal Ethics Committee has been obtained (S67204; 20/01/2023). Results We expect to enroll 5–15 breastfeeding mothers using medication per year. We will determine the concentration of maternal medicines in human milk and estimate the intake of medicines by the nursing infant through parameters such as daily infant dose (DID) and relative infant dose (RID). We will investigate if medicines with limited available data result in low concentrations in human milk and, subsequently, in minimal exposure in breastfed children. Conclusion The systematic approach of the UmbrelLACT initiative in Belgium to study the concentration of medication in human milk will generate essential data, substantiating evidence-based risk assessments on the use of medicines during lactation. Furthermore, the UmbrelLACT data will contribute to the evaluation of PBPK models.