Azathioprine is an immunosuppressive (a medication that suppresses the activity of the immune system) that is used to prevent organ rejection following transplantation and to treat certain autoimmune conditions.

Firdapse is the first-line treatment for Lambert-Easton myasthenic syndrome (LEMS). When symptoms are not sufficiently controlled with Firdapse, patients may receive long-term treatment with the immunosuppressive medications prednisone and azathioprine.

How azathioprine works

Azathioprine is a pro-drug that the body converts to the active compound 6-mercaptopurine, which inhibits the synthesis of the purines needed to build the genetic material of cells, DNA, and RNA. Because DNA has to be duplicated with each cell division, azathioprine mainly affects rapidly multiplying cells such as immune cells.

LEMS is an autoimmune condition in which the patient’s immune cells attack nerve cells controlling muscle movement. Therefore, inhibiting the generation of new immune cells may reduce the immune system attack on nerve cell endings.

Azathioprine in clinical trials

Azathioprine has been reported to be beneficial to LEMS patients, but it has not been studied in randomized clinical trials.

One retrospective study analyzed data from 47 LEMS patients without small-cell lung cancer (SCLC, with which LEMS is associated in about half of the cases). Forty-four (97%) of the 47 patients were treated with prednisone, in 37 cases (84%) in combination with azathioprine. Twenty-six of the 44 patients initially received plasma exchange therapy in addition to immunosuppressive treatment. Seven patients received repeated courses of intravenous immunoglobulin therapy at three to six weekly intervals because symptoms could not be sufficiently controlled with immunosuppressive therapy. The three patients who did not receive immunosuppressive medications were treated with Firdapse.

The median duration of immunosuppressive treatment was 6.4 years. At final follow-up, 37 out of the 44 patients were still alive, and 29 (78%) still required prednisolone, which was combined with azathioprine in 20 patients (54%). Sustained clinical remission was achieved in 20 (45%) of 44 patients, and all except four required continuous immunosuppressive therapy. Muscle strength scores improved in 88% of treated patients and antibody titers against calcium channels decreased in 52% of patients after treatment.

The researchers concluded that immunosuppressive treatment can lead to clinical remission, but in most cases, patients require continuous medication.

Additional information

The use of azathioprine may increase the risk of lymphoma. Because the medication suppressed the division of cells in the bone marrow, patients can become anemic (have a low red blood cell count) and more susceptible to infections. Other common side effects include nausea, vomiting, and chest pain.


Last updated: July 26, 2019


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