Mycophenolate and methotrexate are better tolerated than azathioprine in myasthenia gravis

Azathioprine is recommended as the first-line steroid-sparing immunosuppressive agent for myasthenia gravis. Mycophenolate and methotrexate are often considered as second-line choices despite widespread consensus on their efficacy. We aimed to gather real-world data comparing the tolerability and reasons for discontinuation for these agents, by performing a national United Kingdom survey of side effects and reasons for discontinuation of immunosuppressants in myasthenia gravis. Of 235 patients, 166 had taken azathioprine, 102 mycophenolate, and 40 methotrexate. The most common side effects for each agent were liver dysfunction for azathioprine (23 %), diarrhoea for mycophenolate (14 %), and fatigue for methotrexate (18 %). Women were generally more likely to experience side effects of immunosuppressants. Azathioprine was significantly more likely to be discontinued than mycophenolate and methotrexate due to side effects. There was no significant difference in treatment cessation due to lack of efficacy. This study highlights the significant side-effect burden of treatment for myasthenia gravis. Mechanisms to reduce azathioprine toxicity should be utilised, however mycophenolate and methotrexate appear to be good treatment choices if teratogenicity is not a concern. Women are disadvantaged due to higher frequency of side effects and considerations around pregnancy and breastfeeding. Treatments with improved tolerability are needed.