Azathioprine for Rheumatoid Arthritis

Azathioprine is a purine antagonist drug that competes with the production of nucleic acids, particularly purines. Azathioprine is better known as a chemotherapeutic agent, but has also shown benefit in the treatment of autoimmune disorders such as rheumatoid arthritis. Azathioprine is commonly used in cases where NSAIDs or aspirin has not adequately controlled the patient’s rheumatoid arthritis. The problem with Azathioprine’s toxicity potential is higher in patients with a low azathioprine-thiopurine methyltransferase (TMPT) and thus are more likely to experience bone marrow suppression.  

Potential side effects may include GI upset, vomiting, diarrhea, and sometimes bone marrow suppression. Due to gastrointestinal effects, it should be taken with food. Azathioprine has a delayed onset of action and important to note that it may take 3-6 weeks to see effect of medication. Due to this delayed effect, Azathioprine is commonly prescribed in conjunction with a corticosteroid like Prednisolone. It is important to note side effect profiles can overlap with these medications.

Dosing for RA: give 2mg/kg by mouth daily for 14-21 days in conjunction with glucocorticoid like prednisolone, then every other day until remission of synovial inflammation

Monach, P. A., Arnold, L. M. and Merkel, P. A. (2010), Incidence and prevention of bladder toxicity from cyclophosphamide in the treatment of rheumatic diseases: A data‐driven review. Arthritis & Rheumatism, 62: 9-21. doi:10.1002/art.25061

Stull, J. W., Evason, M., Carr, A. P., & Waldner, C. (2008). Canine immune-mediated polyarthritis: clinical and laboratory findings in 83 cases in western Canada (1991-2001). The Canadian veterinary journal = La revue veterinaire canadienne, 49(12), 1195–1203.