The complex pattern of selective serotonin reuptake inhibitor (SSRI) excretion into breast milk demonstrates gradient and time course effects. Preliminary infant studies have not demonstrated alternation in growth patterns or neurodevelopment from maternal SSRI use. Stowe and associates evaluated the extent of infant medication exposure through breast-feeding during maternal treatment with paroxetine.

Serum and breast milk samples were obtained from 16 postpartum women after stabilization of maternal paroxetine concentrations for at least 10 days. The mean daily dosage of paroxetine was 23.1 mg per day. A total of 108 breast milk samples and 16 mother and infant serum pairs were obtained. Most of the infants were fully breast-fed and received no supplemental nutrition.

Detectable concentrations of paroxetine were present in all breast-milk samples. Excretion gradient analysis of the samples revealed a significant volume-dependent rate of excretion, with greater paroxetine concentrations in later aliquots of breast milk (hind milk). The time course of excretion into breast milk for paroxetine was determined in women who collected more than three samples in 24 hours. In contrast to previously known data for sertraline, a significant relationship with time course of excretion was not observed. However, there was a significant relationship between maternal daily paroxetine dosage and peak and trough breast-milk concentrations.

Maternal serum was obtained two to five hours after the daily paroxetine dosage, and infant serum samples were obtained one to five hours after nursing. All infant serum samples had undetectable concentrations of paroxetine. There were no reported observable effects in infants attributable to paroxetine.

Results of this study confirm and extend the breast-feeding literature by demonstrating that, similar to other antidepressants studied to date, paroxetine is excreted into human breast milk. The pattern of excretion is similar to those found in previous studies that demonstrated higher concentrations in the more lipophilic hind milk. Despite the inability to find detectable concentrations of paroxetine in infant serum, the consistent presence of paroxetine in breast milk demonstrates that the infant is exposed to the drug.

The authors conclude that maternal use of paroxetine appears to exert no adverse effect on breast-fed infants. Data that quantify infant exposure help to define the risks and benefits for postpartum women who must weigh the risks of infant exposure to psychiatric medication during lactation versus the risk of untreated maternal psychiatric illness.