Azathioprine may increase your risk of developing certain types of cancer, especially skin cancer and lymphoma (cancer that begins in the cells that fight infection). If you have had a kidney transplant, there may be a higher risk that you will develop cancer even if you do not take azathioprine. Tell your doctor if you have or have ever had cancer and if you are taking or have ever taken alkylating agents such as chlorambucil (Leukeran), cyclophosphamide (Cytoxan), or melphalan (Alkeran) for cancer. To decrease the risk that you will develop skin cancer, avoid prolonged or unnecessary exposure to sunlight and wear protective clothing, sunglasses, and sunscreen. Tell your doctor immediately if you notice any changes in your skin or any lumps or masses anywhere in your body.
Some teenage and young adult males who took azathioprine alone or with another medication called a tumor necrosis factor (TNF) blocker to treat Crohn's disease (a condition in which the body attacks the lining of the digestive tract causing pain, diarrhea, weight loss, and fever) or ulcerative colitis (condition in which sores develop in the intestines causing pain and diarrhea) developed hepatosplenic T-cell lymphoma (HSTCL). HSTCL is a very serious type of cancer that often causes death within a short period of time. Azathioprine has not been approved by the Food and Drug Administration (FDA) for the treatment of Crohn's disease or ulcerative colitis, but doctors may sometimes prescribe azathioprine to treat these conditions. If you develop any of these symptoms during your treatment, call your doctor immediately: stomach pain; fever; unexplained weight loss; night sweats or easy bruising or bleeding.
Azathioprine can cause a decrease in the number of blood cells in your bone marrow, which may cause serious or life-threatening infections. The risk that the number of blood cells that you have will decrease is highest if you have a genetic (inherited) risk factor. Your doctor may order a test to see if you have this risk factor before or during your treatment. Taking certain medications may also increase the risk that your blood cells will decrease, so tell your doctor if you are taking any of the following: angiotensin converting enzyme (ACE) inhibitors such as benazepril (Lotensin), captopril, enalapril (Vasotec), fosinopril, lisinopril (Prinivil, Zestril), moexipril (Univasc), perindopril (Aceon), quinapril (Accupril), Ramipril (Altace), or trandolapril (Mavik); trimethoprim and sulfamethoxazole (Bactrim, Septra); and ribavirin (Copegus, Rebetol, Virazole). If you experience any of the following symptoms, call your doctor immediately: unusual bleeding or bruising; excessive tiredness; pale skin; headache; confusion; dizziness; fast heartbeat; difficulty sleeping; weakness; shortness of breath; and sore throat, fever, chills, and other signs of infection. Your doctor will order tests before, during, and after your treatment to see if your blood cells are affected by this medication.
What special precautions should I follow?
Before taking azathioprine,
- tell your doctor and pharmacist if you are allergic to azathioprine, any other medications, or any of the ingredients in azathioprine tablets. Ask your doctor or pharmacist for a list of the ingredients.
- tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention the medications mentioned in the IMPORTANT WARNING section and any of the following: allopurinol (Zyloprim); aminosalicylates such as mesalamine (Apriso, Asacol, Pentasa, others), olsalazine (Dipentum), and sulfasalazine (Azulfidine); and anticoagulants ('blood thinners') such as warfarin (Coumadin). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
- tell your doctor if you have any type of infection, or if you have or have ever had kidney disease.
- tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. You should use birth control to be sure you or your partner will not become pregnant while you are taking this medication. Call your doctor if you or your partner become pregnant while you are taking azathioprine. Azathioprine may harm the fetus.
- if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking azathioprine.
- do not have any vaccinations during or after your treatment without talking to your doctor.
Azathioprine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:
Some side effects can be serious. If you experience any of the following symptoms or those listed in the IMPORTANT WARNING section, call your doctor immediately.
- muscle pain
Azathioprine (1.0 to 2.5 mg/kg/day) used among patients with non‐active Crohn's disease is effective for reducing the risk of disease recurrence over a 6 month to 2 year period. Higher doses of azathioprine (2.5 mg/kg/day) are more effective than lower doses (1.0 or 2.0 mg/kg/day) for preventing disease recurrence. There is also evidence that azathioprine may reduce the need for steroid treatment which could help reduce steroid related side effects. Azathioprine appears to be more effective than 6‐mercaptopurine but this may be due to the relatively low dose of 6‐mercaptopurine (50 mg/day) used in the one study assessing this drug. The long‐term effectiveness of azathioprine and 6‐mercaptopurine is unclear due to the short duration of the studies (6 months to 2 years). Azathioprine and 6‐mercaptopurine appear to be slow acting drugs. They are associated with some uncommon but serious side effects. These include suppression of the body's ability to produce white blood cells (which fight infection) and platelets (which allow blood clotting to occur), inflammation of the pancreas and an increased risk of lymphoma. Patients who may benefit from this therapy include those whose Crohn's disease is chronically active or flares frequently. Azathioprine or 6‐mercaptopurine may also benefit patients who are dependent on steroids but have experienced steroid side effects, or for whom steroids no longer work. The choice to use azathioprine or 6‐mercaptopurine should be made after careful consideration of the risks and benefits of using these drugs.