Do you discontinue or adjust azathioprine when a patient develops elevated MCV after starting it?

Great question, with practical implications for the clinic:

Azathioprine (AZA) is a prodrug that likely exerts its immunosuppressive effects against B- and T-cell function by interfering with purine metabolism through its metabolites (including 6-MP).

Logically, many of the "classic" AZA side effects (such as GI toxicity, hair loss, and bone marrow suppression) likely reflect this interference with DNA, RNA, and protein synthesis. In addition to this mechanism of toxicity, AZA hepatic toxicity m...

Interesting discussion but analogously, there are different ways to approach elevated MCV in patients on MTX.

Usually, in patients on AZA, there are alternate immunosuppressant agents to use.