Azathioprine - Pregnancy and Breastfeeding

Pregnancy and Breastfeeding

Azathioprine causes birth defects. A 2003 population-based study in Denmark showed that the use of azathioprine and related mercaptopurine resulted in a seven-fold incidence of fetal abnormalities as well as a 20-fold increase in miscarriage. Birth defects in a child whose father was taking azathioprine have also been reported. Although no adequate and well-controlled studies have taken place in humans, when given to animals in doses equivalent to human dosages, teratogenesis was observed. Transplant patients already on this drug should not discontinue on becoming pregnant. This contrasts with the later-developed drugs tacrolimus and mycophenolate, which are contraindicated during pregnancy.

Traditionally, as for all cytotoxic drugs, the manufacturer advises not to breastfeed whilst taking azathioprine. However, the "Lactation Risk Category" reported by Thomas Hale in his book "Medications and Mothers' Milk" lists azathioprine as "L3", termed "moderately safe"; some recent studies also indicate that breastfeeding does not need to be withheld as the immediate benefits may outweigh the risks. In support of this view, recent research has indicated that thiopurines are not secreted into breast milk.