Addressing maternal medication use during breastfeeding using clinical resources and a novel physiologically based pharmacokinetic model-derived metric: A qualitative study.

Introduction: Breastfeeding has major benefits to the maternal-infant dyad and yet healthcare providers have expressed uncertainty about advocating breastfeeding when mothers are taking medications. The tendency for some providers to be more cautious in their advising approach is likely a consequence of limited, unfamiliar, and unreliable existing information on medication use during lactation. A novel risk metric termed the Upper Area Under the Curve Ratio (UAR) was developed to overcome existing resource shortcomings. However, the perception and use of the UAR in practice by providers is not known. The aim of this study was to understand existing resource use and potential UAR use in practice, their advantages and disadvantages, and areas of improvement for the UAR. Methods: Healthcare providers mainly practicing in California with experience advising on medication use during lactation were recruited. One-on-one semi-structured interviews that included questions on current practices when advising medication use during breastfeeding, and approaches to a given a scenario with and without information about the UAR were conducted. The Framework Method was applied for data analysis to construct themes and codes. Results: Twenty-eight providers representing multiple professions and disciplines were interviewed. Six main themes emerged: (1) Current Practice Approaches, (2) Advantages of Existing Resources, (3) Disadvantages of Existing Resources, (4) Advantages of the UAR, (5) Disadvantages of the UAR, and (6) Strategies to Improve the UAR. Overall, 108 codes were identified that illustrated theme topics ranging from a general lack of metric use to the realities of advising. A workflow describing current practice approaches connected all other themes. Almost all disadvantages of existing resources could be overcome by advantages of other resources and the UAR. Several improvements to the UAR were identified to address its shortcomings. Conclusion: Through interviews with providers who use resources to advise on medication use during breastfeeding, an improved understanding of current practice approaches and accessed resources was ascertained. Ultimately, it was found that the UAR would confer multiple benefits over existing resources, and improvements of the UAR were identified. Future work should focus on implementing the suggested recommendations to ensure optimal uptake of the UAR to improve advising practices.

Infant drug exposure via breast milk.

More than half of women take medications during breastfeeding, predisposing their infants to medication exposure via breast milk. As a result, adverse drug reactions may emerge in the infant, although they are rarely reported. Disposition of maternal drugs in breast milk is described with several key parameters, which include relative infant dose (RID): infant drug intake via milk (weight- and time-adjusted) expressed as a percentage of the similarly adjusted mother's dose. Most drugs show RID values of <10%, indicating that drug concentrations in infant serum do not reach a level known to be therapeutic in adults unless drug clearance is markedly lower than the adult level on a weight basis. RID is a function of milk-to-(maternal) plasma drug concentration ratio (MP ratio) and maternal drug clearance. Therefore, MP ratio between drugs must be interpreted not by itself but with maternal drug clearance of each drug. This is why some drugs such as phenobarbital show an MP ratio of <1 but an RID as high as 50-70%, while morphine shows an MP ratio of 2 but an RID in the range of 5%. Using RID, we interpreted case reports of infant adverse outcomes, and we observed cases with relatively low infant serum concentrations of drug, consistent with low RID, as well as those with near- or above-adult therapeutic serum concentrations, with or without increased drug intake (i.e. high RID). It is important to consider both pharmacokinetic and pharmacodynamic factors in interpreting adverse outcomes in infants breastfed by a mother taking medications.