Is breastfeeding safe with azathioprine?

Background: Azathioprine is commonly used as an immunosuppressant during pregnancy in the management of various conditions such as connective tissue disorders inflammatory bowel disease and pregnant women with organ transplant. Continuation of azathioprine through pregnancy and postpartum is vital for maternal reasons. However there is limited evidence regarding safety of use of azathioprine with breastfeeding. Methods and results: We report an observational case series of 10 mother-baby pairs managed at a tertiary teaching hospital. Mothers on azathioprine who were keen to breastfeed were counselled antenatally regarding limited short term and long-term safety data for the babies. Mothers participating in this study completed a questionnaire at every visit. At follow up visits babies were examined by a neonatologist for clinical signs of infection and checked for adverse effects on haematological profile. Conclusion: There was no clinically significant adverse effect on haematological profile or immunosuppression in these babies. Our case series supports safety of azathioprine in the short term. However large numbers are needed to determine long-term safety of azathioprine and breastfeeding.