Measurement of Atrial Natriuretic Peptide (ANP) Concentrations in Human Breast Milk and Maternal Plasma During Carperitide Therapy (Two Case Reports)

INTRODUCTION: Our institution provides a lactation-medication consultation service for assessing drug transfer into breast milk and determining the appropriateness of breastfeeding. Information for lactating women in Japanese package inserts is often limited, especially for drugs used only in Japan. Carperitide is not approved for use outside Japan, and less is known about its transfer into breast milk or its safety when administered in infants. We report two cases in which atrial natriuretic peptide (ANP) concentrations during carperitide therapy in breast milk and maternal blood were measured. CASE PRESENTATION: We measured ANP concentrations in breast milk and maternal plasma in two postpartum women with peripartum cardiomyopathy to evaluate the transfer of carperitide into breast milk. The breast milk concentration was 0.308 ng/ml in Case 1, and the mean concentration in Case 2 was 1.680 ± 0.055 ng/ml; the relative infant dose was 0.24% and 0.19%-0.53% for Cases 1 and 2, respectively. As the assay cannot distinguish between endogenous ANP and exogenous carperitide, the measured values represent the total ANP levels. During carperitide administration, breast milk ANP concentrations did not exceed the corresponding maternal plasma concentrations or the baseline breast milk levels when carperitide was not administered, suggesting that they remained within the range of endogenous ANP levels. CONCLUSION: The amount of carperitide transferred in these cases was low, potentially mitigating the risk of clinical effects on the infant.