@mmr1984, I would trust my doctor to make the right decision. I also think that our insurance likes us to go with the generic because it is cheaper with usually the same treatment success. Your doctor will likely be ordering frequent blood labs (at least in the beginning) to monitor this medication.
I did not take Imuran for very long. I probably took prednisone for 4-5 months, and then Imuran to reduce the prednisone for a couple weeks. My situation was complicated because we were searching for a diagnosis for my rare liver disease. And AIH (autoimmune hepatitis) was a possible diagnosis. I did not have AIH so the treatment was halted.

Why does the doctor want to add the Imuran?