Monoclonal Antibodies During Breastfeeding—Challenges With Relative Infant Dose

Summary Problems With Current Research Practice Relative infant dose (RID) for monoclonal antibodies (mAbs) is frequently incorrectly calculated and often misleadingly low. RID is not a useful predictor for infant mAb exposure due to different maternal and infant exposure routes, long half‐lives and unknown infant oral bioavailability. The Authors' Opinions Measurement of breast milk concentrations of mAb is of value; however, the use of RID in scientific publications should be abandoned. In future research, systemic exposure should be assessed by measuring infant plasma concentration and calculating the infant‐to‐maternal ratio. Proposed Future Research Priorities Future research should prioritize studies on the transmammary transfer of mAbs, infant intestinal absorption, potential local effects in infant gut, and short‐ and long‐term safety of mAbs for exposed infants.