Used primarily in the treatment of rheumatoid arthritis as a disease-modifying antirheumatic drug (DMARD). It works by suppressing the overactive immune response that causes joint inflammation and damage. Administered via intramuscular injection, it is typically reserved for patients who do not respond adequately to first-line therapies like methotrexate. Its use has declined in recent years due to the availability of biologic agents with fewer side effects, but it remains an option in certain clinical settings. Regular monitoring of blood and urine is required during therapy due to potential toxicity, particularly to the kidneys and bone marrow.