To the Editor: Clinicians treating new mothers for depression require information about the safety of antidepressants if used while the mothers are breast-feeding. In contrast to extensive data on the use of selective serotonin reuptake inhibitor (SSRI) antidepressants by women who are breast-feeding (1–4), we know of only one small case series (N=3) on the use of venlafaxine by breast-feeding mothers (5). In this report, the estimated mean dose the infants received from breast milk was 7.6% of the maternal weight-adjusted dose. No adverse effects were noted in the infants, but the authors cautioned that this dose was high compared to the doses infants are estimated to receive when exposed to other antidepressants through breast milk. To add to the limited available data, we describe results we obtained for two mother-infant pairs in which the mothers were taking venlafaxine while breast-feeding.

Two nursing women taking stable daily doses of venlafaxine provided written informed consent for measurement of their and their infants’ serum levels of the drug. The analysis of venlafaxine and its metabolite, O-desmethylvenlafaxine, was accomplished by means of high-performance liquid chromatography, which has a detection limit of 10 ng/ml.

At birth, the pair 1 infant weighed 3.3 kg and had a gestational age of 37 weeks. The pair 2 infant weighed 3.9 kg and had a gestational age of 38 weeks at birth. Both infants received breast milk exclusively during their first 6 months. The pair 1 mother began taking venlafaxine (75 mg/day) on the day of delivery, while the pair 2 mother took the medication (150 mg/day) throughout her pregnancy. The pair 1 infant was 3 weeks old and weighed 4.1 kg when the serum testing was performed; the pair 2 infant was 4 weeks old and weighed 4.6 kg. The interval between the time the mother took her oral dose and blood was drawn for serum testing was 3.0 hours for pair 1 and 2.0 hours for pair 2. The mothers’ serum medication concentrations were 31.00 and 28.00 ng/ml, respectively, and their serum metabolite concentrations were 148.00 and 230.00 ng/ml. Venlafaxine was not detectable in either infant (0.00 ng/ml in both infants), but the metabolite was present in both children: pair 1 infant, 16.00 ng/ml; pair 2 infant, 21.00 ng/ml. No adverse sequelae, such as changes in sleep, feeding patterns, or behavior, occurred in the infants, as shown by maternal reports and review of pediatric records. In addition, the pediatric records indicated that the children’s weight and heights were in the 85th–100th percentiles.

These findings show that the venlafaxine metabolite was present at low but detectable concentrations in infants exposed to venlafaxine while nursing. The presence of the metabolite suggests that these young infants were able to desmethylate the parent drug. It is encouraging that they did not experience adverse effects from venlafaxine exposure through breast milk and that their development over the first year appeared to be normal.