Azathioprine treatment during lactation SIRS, We read with interest the article by Christensen et al. demonstrating a low penetration of mercaptopurine in maternal milk of eight inflammatory bowel disease (IBD) patients on azathioprine. On the basis of this reported low exposure of children to azathioprine (<1% of the maternal dose), breastfeeding during azathioprine therapy seems safe. This study is of great importance as little is known about breastfeeding by IBD patients on azathioprine. However, considerable inter-individual variability in the absorption and metabolism of azathioprine 3 makes it difficult to predict whether this very low dose in maternal milk would not eventually result in a clinically relevant cumulative dose in the individual child. Therefore, we proposed to monitor the azathioprine metabolites levels in the breastfed child as studied earlier. We wanted to demonstrate the feasibility of this approach in the case of a child born to a 31-year old mother with Crohn‘s disease. The child was fed maternal milk during the 3 months while the mother was treated with azathioprine, 100 mg a day (1.4 mg ⁄ kg). At day 8 of the breastfeeding, the peripheral blood levels of 6-methylmercaptopurine (6-MMP) and 6-tioguaninenucleotides (6-TGN) were assessed in the child; both appeared undetectable. At month 3, when the feeding with maternal milk was tapered to zero, the levels of 6-MMP and 6-TGN were again undetectable in the child, while the mother had therapeutic levels (6-MMP 410 pmol ⁄ 10 red blood cells, 6TGN 470 pmol ⁄ 10 red blood cells). During the 6 months of the follow-up, the child thrived and did not suffer from any infections. Thus, breastfeeding by IBD patients on azathioprine is probably safe. However, until more experience is gained, we advocate the monitoring of azathioprine metabolites as a method to safeguard the minimal exposure of a breastfed child.
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