Transfer of the antidepressant mirtazapine into breast milk

Kristensen JH, Ilett KF, Rampono J, Kohan R, Hackett LP.
Br J Clin Pharmacol. 2007 Mar;63(3):322-7. Epub 2006 Sep 13.


What is already known about this subject

  • There is presently only a single case report on mirtazapine transfer into breast milk and its effects in the breast-fed infant.

What this study adds

  • Most importantly, we have provided quantitative data on the absolute and relative infant doses of mirtazapine and its active metabolite.
  • We have also documented a lack of overt adverse effects in the breast-fed infants and low or absent plasma concentrations of mirtazapine in a subset of these infants.
  • Hence we now know that breast-fed infants are unlikely to be adversely affected when their mothers need to take mirtazapine.

Aims To investigate the transfer of mirtazapine and desmethylmirtazapine into milk and to calculate dose to the infant via milk.

Methods Plasma and milk samples were obtained from eight breast-feeding women who were taking a median dose of 38 mg mirtazapine per day. Milk/plasma ratio (M/P) and infant doses were estimated by standard methods. The infants were examined clinically and in four infants blood was taken for analysis.

Results Mean (95% confidence interval) relative infant doses for mirtazapine and desmethylmirtazapine (n = 8) were 1.5% (0.8, 2.2) and 0.4% (0.2, 0.6) respectively. The mean M/P (area under curve n = 4, single or paired samples n = 3) was 1.1 (0.7,1.5) for mirtazapine and 0.6 (0.5, 0.7) for desmethylmirtazapine. No adverse effects were seen. Mirtazapine was detected (1.5 µg l−1) in only one of four infants tested.

Conclusion We suggest that mirtazapine use by lactating women is safe for the breast-fed infant. Nevertheless, each decision to breast feed should always be made on the basis of an individual risk/benefit analysis.

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