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.
Dr Christensen and colleagues from Denmark estimated the exposure of breastfed infants to mercaptopurine, as a metabolite of azathioprine, from maternal milk.
The team assessed 8 lactating women with inflammatory bowel disease receiving maintenance therapy with azathioprine 75-200 mg daily.
The researchers obtained milk and plasma samples 30 and 60 min after drug administration and hourly for the following 5 hours.
|Infant ingests mercaptopurine of less than 0.008 mg/kg bodyweight/24 hours|
|Alimentary Pharmacology & Therapeutics|
The variation in the bioavailability of the drug was reflected in a wide range of peak plasma values of mercaptopurine within the first 3 hours.
A similar curve, but with an hour's delay and at significantly lower concentrations varying from 2 to 50 µg/L, was seen in maternal milk.
After 6 hours, the research team measured an average of 10% of the peak values.
Dr Christensen's team concludes, "The major part of mercaptopurine in breast milk is excreted within the first 4 hours after drug intake."
"On the basis of maximum concentration measured, the infant ingests mercaptopurine of less than 0.008 mg/kg bodyweight/24 hours."
"The findings confirm that breastfeeding during treatment with azathioprine seems safe and should be recommended, considering the extensive beneficial effects."