Azathioprine treatment during lactation

Aliment Pharmacol Ther. 2008 Nov 15;28(10):1209-13. doi: 10.1111/j.1365-2036.2008.03843.x. Epub 2008 Aug 30.


Background: Thiopurines are widely used to maintain remission in inflammatory bowel disease. Treatment during pregnancy is generally recommended to improve the chance of a normal birth outcome, but advice concerning breastfeeding is conflicting. Aim To estimate the exposure of breastfed infants to 6-mercaptopurine, as a metabolite of azathioprine, from maternal milk.

Methods: Eight lactating women with inflammatory bowel disease receiving maintenance therapy with azathioprine 75-200 mg daily were studied. Milk and plasma samples were obtained 30 and 60 min after drug administration and hourly for the following 5 h.

Results: The variation in the bioavailability of the drug was reflected in a wide range of peak plasma values of 6-mercaptopurine within the first 3 h. A similar curve, but with an hour's delay and at significantly lower concentrations varying from 2-50 microg/L, was seen in maternal milk. After 6 h an average of 10% of the peak values were measured.

Conclusions: The major part of 6-mercaptopurine in breast milk is excreted within the first 4 h after drug intake. On the basis of maximum concentration measured, the infant ingests mercaptopurine of <0.008 mg/kg bodyweight/24 h. The findings confirm that breastfeeding during treatment with azathioprine seems safe and should be recommended, considering the extensive beneficial effects.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Azathioprine / pharmacokinetics
  • Azathioprine / therapeutic use*
  • Breast Feeding*
  • Female
  • Humans
  • Immunosuppressive Agents / pharmacokinetics
  • Immunosuppressive Agents / therapeutic use*
  • Inflammatory Bowel Diseases / drug therapy*
  • Lactation / drug effects*
  • Milk, Human / drug effects*
  • Milk, Human / metabolism
  • Pregnancy


  • Immunosuppressive Agents
  • Azathioprine