Hi Ravenclaw

Imuran is an immunosuppression drug. It works by blocking DNA synthesis so its effects are largely confined to rapidly dividing cells. Activated T and B cells divide rapidly and play key roles in the immune system response to infections. Imuran stops them from dividing which explains why it is an immunosuppressant.

Imuran can also stop bone marrow stem cells from dividing. These stem cells produce all of the different kinds of peripheral blood cells. That is why your clinical care team will want to do a Full Blood Count (measuring the numbers of all of your different peripheral blood cells), to check out that possible side-effect.

This fairly technical free-access paper might help you to learn more about current therapies for myasthenia gravis - it could help you to ask your clinical care team informed questions; http://www.ncbi.nlm.nih.gov/pubmed/24117026 .