Hi, Ricardo. I am about to go on azathiopine, too. I don't know about long-term effects, but I know two important things:

1) Your doctor should give your wife a blood test called the TPMT test before she starts the drug. It is to make sure she has the enzyme needed to metabolize it. http://www.medscape.com/viewarticle/586270

2) Your wife will need blood tests regularly while taking the drug--often at first, and then less often. These are to make sure it's not harming her liver or blood count.

Abby