Use only preservative-free Methotrexate Injection for treatment of neonates or low birth weight infants and for intrathecal use. Learn about Rasuvo® (methotrexate) injection, an RA treatment option. Access co-pay cards, RA Coach, and patient support for an RA auto-injector. Methotrexate is injected 1 day a week, on the same day of the week. For instance, if you give yourself the first injection on a Saturday morning, you will repeat the injection the next Saturday morning, and every Saturday morning after that. Methotrexate Injection: learn about side effects, dosage, special precautions, and more on MedlinePlus Methotrexate is a medication commonly used in the treatment of Rheumatoid Arthritis, Psoriatic Arthritis, and other autoimmune conditions. It works by suppressing abnormal high activity of your immune system to reduce inflammation, swelling, and damage to your joints. Methotrexate injection is used in combination with other cancer treatments to treat gestational trophoblastic neoplasia and breast cancer in adults. Methotrexate injection is also used alone to treat squamous cell carcinoma of the head and neck in adults. Methotrexate injection may be given by the intramuscular, intravenous or intra-arterial route. However, the preserved formulation contains Benzyl Alcohol and must not be used for intrathecal or. Methotrexate injection is used alone or together with other medicines to treat several types of cancer, such as breast, head and neck, lung, blood, bone, lymph node, and uterus cancers. Methotrexate, formerly known as amethopterin, is a chemotherapy agent and immune-system suppressant. It is used to treat cancer, autoimmune diseases, and ectopic pregnancies. Methotrexate treats certain leukemias and lymphomas, mycosis fungoides, rheumatoid arthritis, polyarticular juvenile idiopathic arthritis in children, and severe psoriasis in adults. Learn about side effects, interactions, and indications.