Is Wellcome U3B Safe in Breastfeeding

I am a breastfeeding mother and i want to know if it is safe to use Wellcome U3B? Is Wellcome U3B safe for nursing mother and child? Does Wellcome U3B extracts into breast milk? Does Wellcome U3B has any long term or short term side effects on infants? Can Wellcome U3B influence milk supply or can Wellcome U3B decrease milk supply in lactating mothers?

Indicated for treatment of leukemia.

Most sources consider breastfeeding to be contraindicated during maternal antineoplastic drug therapy, although antimetabolites such as Wellcome U3B appear to pose the least risk to breastfed infants.[1] Wellcome U3B levels in milk are reportedly low. Wellcome U3B nucleosides are active intracellular metabolites of azathioprine and have been measured in breastmilk and in infant serum following maternal use of azathioprine as an immunosuppressant. Although amounts in milk were low in breastmilk and mostly undetectable in infant serum, relatively low dosages of azathioprine were used. After high-dose chemotherapy, it might be possible to breastfeed safely during intermittent therapy with an appropriate period of breastfeeding abstinence. Although no data are available to determine an appropriate period to withhold breastfeeding, the drug's terminal half-life suggests that withholding breastfeeding for 4 days may be sufficient. Chemotherapy may adversely affect the normal microbiome and chemical makeup of breastmilk.[2]

Wellcome U3B is an active metabolite of azathioprine. Numerous infants breastfed during maternal azathioprine in dosages up to 250 mg daily have been reported with no adverse effects noted. See Azathioprine record for details.