Fluoxetine and norfluoxetine concentrations in nursing infants and breast milk

Background: This study's goal was to characterize nursing infants' exposure to fluoxetine through breast milk and to identify variables for minimizing such exposure. Methods: Nursing women on stable daily doses of fluoxetine were recruited i nto the study. Breast milk, maternal and infant serum concentrations of flu oxetine and norfluoxetine were determined with high-performance liquid chro matography. Results: Nineteen. nursing women (one with a pair of dizygotic twins) parti cipated in the study. The women were on stable daily doses of fluoxetine (1 0-60 mg/day) and all but two took the medication during the last trimester of pregnancy. Fluoxetine was detectable in 30% (n = 6) of the nursing infan t sera (< 1-84 ng/mL), whereas norfluoxetine was found in 85% (N = 17) (< 1 -265 ng/mL). Peak breast milk concentrations occurred approximately 8 hours after maternal dosing and predicted norfluoxetine concentrations in infant sera-fm. Maternal serum fluoxetine and norfluoxetine concentrations correl ated highly with infant norfluoxetine concentrations. A daily maternal fluo xetine dosage of 20 mg or lower was significantly less likely to produce de tectable concentrations of either fluoxetine or norfluoxetine in infants co mpared to higher daily dosages. No adverse effects were reported in any inf ant. Conclusions: Our findings demonstrate that maternal serum and peak breast m ilk concentrations of fluoxetine and norfluoxetine predict nursing infant s erum norfluoxetine concentrations. In nursing women taking 20 mg/day or les s of fluoxetine, infant serum concentrations were typically lolly. (C) 2001 Society of Biological Psychiatry.