Azathioprine is an immunosuppressant used to treat moderate to severe lupus, especially when major organs like the kidneys, lungs, or blood cells are involved. It works by reducing the activity of the immune system to prevent flares and limit inflammation.

It is often used as a steroid-sparing agent to reduce the need for long-term corticosteroids. Azathioprine is generally well tolerated but requires regular monitoring for blood counts and liver function, as it can cause bone marrow suppression and liver toxicity. It’s commonly used in lupus nephritis, during pregnancy, or when other immunosuppressants are not tolerated.