Limited information indicates that maternal doses of up to 120 mg daily produce low levels in milk and would not be expected to cause any adverse effects in breastfed infants, especially if the infant is older than 2 months. If mirtazapine is required by the mother, it is not a reason to discontinue breastfeeding. Exclusively breastfed infants should be monitored for behavioral side effects and adequate growth if this drug is used during lactation.
A woman who was 14 weeks postpartum was started on mirtazapine 30 mg daily. After reaching steady-state (therapy duration not specified), a foremilk level of 7 mcg/L and hindmilk level of 18 mcg/L were measured 22 hours after the previous dose. The next day, a foremilk level of 28 mcg/L and hindmilk level of 34 mcg/L were measured 15 hours after the previous dose.
Eight nursing mothers who averaged 6.3 months postpartum (range 1.5 to 13 months) were taking mirtazapine in an average dosage of 495 mcg/kg daily (30 to 120 mg daily). Mothers provided milk samples every 3 to 4 hours for 24 hours after their daily dose. Using these data, the authors estimated that an exclusively breastfed infant would receive an average of 8 mcg/kg daily of mirtazapine and 3 mcg/kg daily of desmethylmirtazapine. These values averaged 1.5% (range 0.6 to 2.8%) of the maternal weight-adjusted dosage for mirtazapine and 0.4% (range 0.1 to 0.7%) for desmethylmirtazapine. Mirtazapine's concentration in hindmilk averaged 2.3 times the foremilk concentration in 4 of the subjects tested. Desmethylmirtazapine's concentration in hindmilk was only 10% higher than in foremilk.
A woman who was 6 weeks postpartum was taking mirtazapine 22.5 mg daily at night. Foremilk and hind milk levels of mirtazapine were 130 and 145 mcg/L, respectively, at 4 hours after the dose and 61 and 90 mcg/L at 10 hours after the dose.
A woman took mirtazapine 15 to 30 mg daily throughout the second and third trimesters of pregnancy and during breastfeeding. Her postpartum dose was 15 mg daily or 224 mcg/kg daily. In the morning, 12 hours after the dose, the concentration of mirtazapine in her foremilk was 15 mcg/L.
A woman who was 14 weeks postpartum was started on mirtazapine 30 mg daily. The patient breastfed her 6.8 kg infant 6 times daily during therapy and an infant plasma level of 0.2 mcg/L was found 15 hours after a dose.
Eight infants who averaged 6.3 months of age (range 1.5 to 13 months) were breastfed (extent not stated) by mothers taking mirtazapine in an average dosage of 495 mcg/kg daily for 6 to 129 days. No mirtazapine or desmethylmirtazapine were detected (<1 mcg/L) in the serum of 4 infants whose mothers' doses ranged from 309 to 517 mcg/kg daily. Three others had unquantifiably low levels in milk. One infant, whose mother was taking 1967 mcg/kg daily, had 1.5 mcg/L of mirtazapine in serum, but an unquantifiable serum level of the metabolite.
A 2-month-old infant was breastfed (extent not stated) by a mother who was taking mirtazapine 15 mg (224 mcg/kg) daily at night. The infant's serum mirtazapine concentration at 2 hours after the first morning feeding (14 hours after the previous maternal dose) was 10 mcg/L compared to a maternal serum mirtazapine concentration of 27 mcg/L at 12 hours after the previous dose.
Effects in Breastfed Infants:
A 14-week old infant was breastfed 6 times daily during maternal treatment with mirtazapine 30 mg daily. After 6 weeks of therapy, the infant was judged to have normal psychomotor development and no adverse effects, including sedation or abnormal weight gain.
Eight infants who averaged 6.3 months of age (range 1.5 to 13 months) were breastfed by mothers taking mirtazapine in an average dosage of 495 mcg/kg daily for 6 to 129 days. At the time they were studied, the average Denver developmental age in the 7 infants studied averaged 101% of normal. No adverse effects were noted in any of the infants.
A 6-week-old infant was exclusively breastfed by a mother who was taking mirtazapine 22.5 mg at daily at night beginning at 4 weeks postpartum. Weekly follow-ups of the infant found no sedation or alterations in weight gain, although the infant's weight was consistently below the 25th percentile even before mirtazapine was begun.
A 2-month-old infant was breastfed (extent not stated) by a mother taking 15 mg of mirtazapine daily during pregnancy and lactation. The mother stated that the infant had a higher birthweight and gained weight more rapidly than her previous 3 infants, and that unlike her other infants, this infant slept through the night at this age. The authors noted that these observations cannot necessarily be attributed to mirtazapine.
Possible Effects on Lactation:
Gynecomastia, hyperprolactinemia and galactorrhea were reported in an 89-year-old man after 21 months of therapy with mirtazapine 30 mg daily. Symptoms regressed 1 month after discontinuation and prolactin levels normalized. The clinical relevance of these findings in nursing mothers is not known. The prolactin level in a mother with established lactation may not affect her ability to breastfeed.
1. Aichhorn W, Whitworth AB, Weiss U et al. Mirtazapine and breast-feeding. Am J Psychiatry. 2004;161:2325. Letter. PMID:15569912 2. Kristensen JH, Ilett KF, Rampono J et al. Transfer of the antidepressant mirtazapine into breast milk. Br J Clin Pharmacol. 2007;63:322-7. PMID:16970569 3. Klier CM, Mossaheb N, Lee A, Zernig G. Mirtazapine and breastfeeding: maternal and infant plasma levels. Am J Psychiatry. 2007;164:348-9. PMID:17267804 4. Tonn P, Reuter SC, Hiemke C, Dahmen N. High mirtazapine plasma levels in infant after breast feeding: case report and review of the literature. J Clin Psychopharmacol. 2009;29:191-2. PMID:19512989 5. Lynch A, Madjlessi A. [Gynecomastia-galactorrhea during treatment with mirtazapine]. Presse Med. 2004;33:458. Letter. PMID:15105766
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