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* Departments of Psychiatry
Obstetrics/Gynecology
Laboratory Medicine, Yale University School of Medicine, New Haven, Connecticut
|| Yale Child Study Center Yale University School of Medicine, New Haven, Connecticut
| ABSTRACT |
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Methods. Maternal and infant transporter blockade was assessed by measurement of platelet 5-HT in 11 breastfeeding mother-infant pairs before and after 4 to 12 weeks of maternal fluoxetine (2040 mg/d) treatment for postpartum depression. The study was approved by the Human Investigation Committee of Yale University School of Medicine, and each mother (mean age: 34.5 years; standard deviation [SD]: 5.3) gave written informed consent. Whole-blood 5-HT levels and plasma fluoxetine and norfluoxetine levels were determined by high-performance liquid chromatography.
Results. Five mothers were taking 20 mg of fluoxetine daily, 4 were taking 30 mg daily, and 2 were taking 40 mg daily. Mean infant age at the start of the study was 16.8 (SD: 8.8) weeks. All infants except 1 were <6 months of age and 4 were <3 months of age when their mothers began treatment. Six infants were breastfed exclusively; the remaining were breastfed between 3 and 8 times daily and were given supplemental feedings. Mean maternal postexposure 5-HT levels of 22.9 ng/mL (SD: 12.5) were markedly lower than mean preexposure (baseline) levels of 156.6 ng/mL (SD: 71.4; paired t = 6.9, df = 10). In contrast, the mean infant pre- and postexposure 5-HT concentrations of 217.1 (SD: 66.5) and 229.9 (SD: 83.5) ng/mL, respectively, were similar (paired t = 0.24, df = 10). However, the 1 infant with measurable plasma fluoxetine had a substantial decline in 5-HT to 40% of baseline. In samples obtained from the same infant 4 months later, plasma drug levels were undetectable (<1 ng/mL) and the platelet serotonin levels were no longer reduced (12% increase from baseline).
Conclusions. The marked declines (to 9%28% of baseline) in platelet 5-HT concentrations seen in mothers who were treated with the SSRI fluoxetine were similar to those observed in our study of sertraline in breastfeeding and other previous studies. In contrast, all but 1 infant experienced little or no decline in whole-blood (platelet) 5-HT concentrations after exposure to fluoxetine through breast milk. The substantial drop in platelet 5-HT seen in 1 infant and the coupling of this drop with measurable plasma fluoxetine level raises some concern. Possible reasons for the infants measurable plasma fluoxetine level include his mothers high plasma drug level and his being breastfed exclusively. However, the observations may be coincidental, and the infant experienced no discernible adverse effects. These data suggest that most infants may continue to breastfeed without experiencing meaningful changes in platelet 5-HT transport while their mothers are treated with 20 to 40 mg of fluoxetine daily. Given the limited data regarding occurrence and extent of SSRI exposure and the uncertainties concerning the possible effects of exposure, it is premature to propose treatment guidelines. Our own advice to women who are thinking of combining breastfeeding and SSRI treatment will weigh a range of factors, including severity of postpartum depression, any demonstrated preferential response to a specific SSRI, and the mothers commitment to breastfeeding. Additional research is needed to establish more definitively the frequency of physiologically meaningful infant SSRI exposure during breastfeeding and to determine the behavioral consequences of such exposure.
Key Words: fluoxetine breastfeeding postpartum serotonin serotonin transporter platelets
Abbreviations: SSRI, selective serotonin reuptake inhibitor 5-HT, 5-hydroxytryptamine SD, standard deviation
The short- and long-term benefits of breastfeeding for both mothers and infants are well documented.1 It is also apparent that postpartum major depression, a frequently (10%) occurring complication of childbirth, seriously affects the mothers functioning, the mother-infant relationship, and the childs subsequent development and propensity for later psychopathology.24 Although selective serotonin reuptake inhibitors (SSRIs) are effective in treating postpartum depression, concerns have been raised regarding their use in lactating women.
Appreciable drug levels are measured in breast milk of women who receive SSRIs, and plasma drug levels in the low ng/mL range have been reported in their nursing infants.5 Although infant plasma drug levels are low compared with those typically seen in patients, infant levels in some reports do seem to be at or near the drugs reported affinities (KDs) and IC50s for inhibition at the serotonin (5-hydroxytryptamine [5-HT]) transporter.69 The impact of central serotonin 5-HT modulation by SSRIs during critical periods of brain development is unknown. Although 5-HT plays important roles in early neurodevelopment,1014 the preclinical literature regarding the impact of SSRI exposure during neurodevelopment is inconsistent and difficult to generalize to humans.15,16
These concerns have led our group to examine whether exposure through breast milk has a discernible effect on platelet 5-HT uptake. The platelet and neuronal 5-HT transporters are identical with respect to sequence and pharmacologic sensitivities.17,18 All platelet 5-HT is accumulated by uptake through the platelet membrane 5-HT transporter, and a number of studies have used the decline in platelet 5-HT seen after administration of reuptake inhibitors as an index of central and peripheral transporter blockade.1921 Taking advantage of the similarities between platelet and neuronal serotonin transporters,17,18 we used measurements of platelet 5-HT before and during maternal sertraline treatment (50100 mg daily) to determine the degree the 5-HT transporter blockade in breastfed infants.22,23 We found that infants who were exposed to sertraline through their mothers breast milk experienced little to no change in platelet 5-HT levels, suggestive of minimal effects on peripheral and central 5-HT transporter blockade.
The widely prescribed SSRI fluoxetine (Prozac) is often used to treat postpartum depression. Compared with sertraline and other SSRIs, fluoxetine and, in particular, its active metabolite, norfluoxetine, have substantially longer plasma half-lives, and both compounds have been found in measurable quantities in infant plasma.2429 Thus, to extend our previous work in this area, we measured platelet 5-HT levels in breastfeeding mother-infant pairs before and during maternal treatment with fluoxetine.
| METHODS |
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Mothers and infants had blood drawn by venipuncture and heelstick, respectively, for determination of whole-blood 5-HT levels before the mothers initiation of fluoxetine treatment. Mothers then began fluoxetine (initial dose: 20 mg/d) and continued to breastfeed their infants according to their preferred schedule. Postexposure blood sampling occurred 4 to 12 weeks after the initiation of fluoxetine treatment and no sooner than 10 days after a change in fluoxetine dose. All blood samples were obtained between 10 AM and 2 PM, approximately 2 to 4 hours after the last breastfeeding session. Mothers and infant both underwent venipuncture to obtain approximately 5 mL of blood for whole-blood 5-HT and plasma fluoxetine levels. Blood was collected into tubes that contained dipotassium ethylenediaminetetraacetic acid using standard venipuncture techniques. All specimens obtained for whole-blood 5-HT analysis was kept at room temperature, and duplicate or triplicate samples were removed and stored at 70°C; portions were also sent for automated platelet count (Hematology Laboratory, Yale-New Haven Hospital, New Haven, CT).
Whole-Blood 5-HT Analysis
Whole-blood 5-HT levels were determined in duplicate or triplicate by high-performance liquid chromatography with fluorometric detection as previously described.23,30 More than 99% of blood 5-HT is found within the platelet, and whole-blood 5-HT concentrations (ng/mL) can also be expressed on a per-platelet (ng/109 platelets) basis if a whole-blood platelet count is obtained.
Plasma Drug Analysis
Plasma fluoxetine and norfluoxetine levels were determined by reversed-phase high-performance liquid chromatography with ultraviolet detection (202 nm) as previously described.31 Day-to-day (N = 3) coefficients of variation for a 50-ng/mL control sample were 2.0% for fluoxetine and 2.6% for norfluoxetine. Drug levels were first determined in mother and infant plasma using standards ranging from 10 to 100 ng/mL. Results <10 ng/mL were considered semiquantitative, and most infant samples had fluoxetine levels less than the estimated detection limit of 1 ng/mL. For determining drug levels more accurately in an infant (9) plasma with an estimated 2.2 ng/mL of fluoxetine (and 2.7 ng/mL norfluoxetine), a second portion of the plasma sample was reanalyzed using standards ranging from 2 to 8 ng/mL. The standard curve was linear over this range, and, with the use of a control plasma spiked with 2 ng/mL of drug, fluoxetine and norfluoxetine were determined with within-day coefficients of variation (N = 3) of 14% and 4%, respectively. On reanalysis, the levels of fluoxetine and norfluoxetine observed in the infant 9 sample were 2.6 and 2.4 ng/mL, respectively (another reanalyzed infant [6] plasma sample showed <1 ng/mL fluoxetine on both analyses, whereas norfluoxetine levels of 3.6 and 3.0 ng/mL were observed on the first and second analysis, respectively.)
Statistical Analyses
To determine the impact of fluoxetine exposure on 5-HT levels, we conducted paired t tests comparing pre- and postexposure 5-HT levels separately for the mother and infant groups. Pearson correlations were performed to examine the relationship between change in 5-HT levels over time and maternal drug dose, maternal fluoxetine and norfluoxetine levels, age of infant at the start of the study, fluoxetine and norfluoxetine levels, and breastfeeding status (exclusive or partial breastfeeding).
| RESULTS |
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Mean maternal pre- and postexposure 5-HT levels were 157 ng/mL (SD: 71.4) and 23 ng/mL (SD: 12.5), respectively (Table 1, Fig 1). Paired t test revealed a highly significant decline in maternal whole-blood 5-HT levels with fluoxetine treatment (t = 6.9, df = 10, P < .0001). Individual postexposure maternal 5-HT values ranged from 9% to 28% of baseline (mean change to 14.5% [SD: 7%] of baseline). In contrast, the mean infant pre- and postexposure 5-HT concentrations of 217 ng/mL (SD: 66.5) and 230 ng/mL (SD: 83.5), respectively, were similar (paired t = 0.24, df = 10, P = .82). The mean infant individual percentage change from baseline was 3.6% (99% confidence interval: 26% to 33%). Infant age at the start of the study, maternal fluoxetine dose, maternal fluoxetine and norfluoxetine plasma levels, and exclusivity of breastfeeding did not correlate with change in infant 5-HT levels. Similar results for group comparisons and correlative analyses were obtained when 5-HT levels were expressed as ng/109 platelets.
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| DISCUSSION |
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The apparent absence of platelet 5-HT transporter blockade in most nursing infants of mothers who were being treated with fluoxetine is consistent with our previous findings with breastfeeding infants who were exposed to sertraline. However, the substantial drop in platelet 5-HT seen in infant 9 stands apart, and we believe that this observation deserves mention, especially considering the rebound in platelet serotonin levels after the reduction in breastfeeding. Although the coupling of this drop in platelet 5-HT with measurable plasma fluoxetine in a single infant raises concerns, the findings may be coincidental, and it is important to note that this infant experienced no discernible adverse effects. Possible reasons for the observable plasma fluoxetine level in infant 9 include the high maternal drug level and the infants being breastfed exclusively; no viral infection was apparent at the time of blood draw. The explanations offered for the higher plasma drug level in infant 9 are conjectural, and we want to be careful not to overemphasize the significance of the observations in this 1 infant.
This infant as well as infants 3, 4, 5, 6, 7, and 11 participated in a parallel study of the impact of in utero and/or breastfeeding exposure to SSRIs on infant development. Bayley Scale scores conducted in these infants (age range: 2456 weeks) revealed that all but 1 were within 1 SD of the mean on mental and motor developmental indices. Infant 7 scored an 82 (mild delay) on the motor index and a 92 (normal range) on the mental index at 24 weeks of age primarily because he was not yet sitting up on his own.
| CONCLUSIONS |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Reprint requests to C. Neill Epperson, MD, Department of Psychiatry, Yale University School of Medicine, University Towers, Ste 2H, 100 York St, New Haven, CT 06511. E-mail: neill.epperson{at}yale.edu
| REFERENCES |
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