Duloxetine transfer across the placenta during pregnancy and into milk during lactation

Duloxetine is an efficacious antidepressant; however, its safety during the perinatal period is uncertain. The objective of
this study was to assess the transfer across the placenta and provide data on infant exposure to duloxetine via breast milk.

A multiparous 31-year-old woman with recurrent melancholic depression had responded poorly to previous antidepressants, but
had a full remission on duloxetine. She elected to remain on duloxetine for her third pregnancy and while breastfeeding. She
gave birth to a healthy term infant and there were no adverse events noted for the infant exposed to duloxetine. Duloxetine
concentration was measured chromatographically in maternal and infant serum collected at birth, and in maternal milk and plasma
and infant plasma 18 days later, (C/M) concentration ratio was calculated. Absolute and relative infant doses via milk were
estimated and the percent drug in infant versus mother’s plasma was calculated.

Cord/maternal serum concentration ratio for duloxetine was 0.12. Absolute infant dose via milk was 7.6 μg/L and relative infant
dose was 0.81%. The ratio of drug in the infant’s plasma to that in maternal plasma during lactation also gave a 0.82% infant
exposure estimate.

The low C/M ratio suggests a limited transfer across the placenta. The relative infant dose via milk was low by comparison
to most other antidepressants, and this estimate confirmed the amount of drug in infant plasma during lactation. Our data
suggest that duloxetine may be used in pregnancy and lactation for selected patients in whom other antidepressants have not
been successful.