Methotrexate is a Disease Modifying Anti-Rheumatic Drug (DMARD) that is also known as Trexall, Folex PFS, Rheumatrex Dose Pack, and Methoxtrexate Sodium.
Low dose methotrexate is a very common treatment for rheumatoid arthritis, psoriatic arthritis, and many other types of arthritis.
Methotrexate is also known as a treatment for cancer. As a cancer treatment, it is prescribed at significantly higher doses than for arthritis treatment. Methotrexate is also occasionally used to treat certain other diseases as well.
Methotrexate is understood to work by altering how the body uses folic acid (vitamin B9), a vitamin that is needed for cell growth.
To treat arthritis, methotrexate is taken once a week. It is available in oral tablet form (2.5 mg tablets) and in liquid injectable form (25 mg/mL vials or pre-filled syringes) for subcutaneous (under the skin) injection.
The standard dose for tablets ranges from 6 per week (15 mg) to 10 per week (25 mg). On the day that it is taken, tablets can be taken all at once or split up and taken twice over a 24 hour period. The standard dose for injection ranges from 0.6 mL (15 mg) to 1.0 mL (25 mg) per week.
Subcutaneous injections are easy to do compared to other types of injections. Patients can do them quickly at home. A small needle pokes just under the skin to deliver medicine into the “fatty tissue” below.
Injected methotrexate has a number of benefits over oral methotrexate. It tends to have fewer side effects like nausea and it is absorbed by the body better and more consistently (85% absorption for injected vs. 20-80% variability for oral). A few small studies have even suggested that the injected form may be a more effective treatment for Rheumatoid Arthritis.
When methotrexate works, most patients start to feel improvement after 6-8 weeks. The maximum effect can take 6-12 months. If a patient starting on methotrexate doesn’t feel any effects after a 3 month “trial period” then the medication is usually stopped.
Important Tests and Risks
Methotrexate is generally a safe medication that is tolerated by most patients who take the low dosages prescribed by rheumatologists to treat arthritis.
Patients should have their blood tested every 1-3 months so their doctor can monitor for potential side effects on the liver or blood counts.
Methotrexate should not be taken with sulfa antibiotics such as co-trimoxazole (Septra) or trimethoprim.
People taking methotrexate should avoid drinking alcohol.
Methotrexate can very rarely cause an unusual lung reaction that is more likely to occur in older patients with underlying lung disease.