Paroxetine in human milk

The primary aims of the study were to estimate the exposure of infants to paroxetine via breast milk and to determine the maternal milk:plasma ratio (M/P) of paroxetine. Secondary aims were to compare single point and area under the curve (AUC) estimates of M/P, to assess variability of M/P in fore and hind milk, and to compare the observed M/P with that predicted by a model.

Two studies were performed. In one study, six nursing mothers who were being treated with paroxetine were studied over a 24 h dose interval at steady-state. The total amount of paroxetine in the milk was measured, which represented the 'dose' to the infant. The M/PAUC was calculated and compared with a predicted value. In the second study, four nursing mothers who were being treated with paroxetine, were studied at steady-state, around a normal infant feeding time. A single plasma sample and a prefeed milk sample were taken approximately 3 h after the morning dose of paroxetine, and a postfeed milk sample taken around 1 h later. The dose received by the infant was estimated from the average milk concentrations of the pre and postfeed samples using standard assumptions, and M/P calculated directly. Plasma concentrations of paroxetine were measured in 8 of the 10 infants in the two studies.

The mean dose of paroxetine received by the infants in the first study was 1.13% (range 0.5-1.7) of the weight adjusted maternal dose. The mean M/PAUC was 0.39 (range 0.32-0.51). The predicted M/P was 0.22. The mean dose of paroxetine received by the infants in the second study was 1.25% (range 0.38-2.24) of the weight adjusted maternal dose. The mean M/P was 0.96 (range 0.31-3.33) and did not differ between fore and hind milk. The drug was not detected in the plasma of seven of the infants studied and was detected but not quantifiable (<4 microg l-1 ) in one infant. No adverse effects were observed in any of the infants.

Measured M/P and estimated infant dose were similar in the two studies, although the range was wider for the single point study. Paroxetine can be considered 'safe' during breast feeding because the dose transferred to the infant is well below the recommended safety limit of 10% of the weight adjusted maternal dose, concentrations in the infants were generally undetectable, and no adverse effects were reported.